^ Standards

• Draft C89 standard
• Draft C99 standard
• Draft C11 standard
• Draft C18 standard

^ Build Systems

• aimake - Build tool designed to avoid complex configurations. GPL 3
• Autoconf - Extensible package of M4 macros that produce shell scripts to automatically configure software source code packages. Part of the Autotools. GPL 2
• Automake - Tool for automatically generating Makefile.in files compliant with the GNU Coding Standards. Requires the use of Autoconf. Part of the Autotools. GPL 2
• Bazel - Build system for various operating systems and targets. Apache 2
• Buck - Build system created and used by Facebook. Apache 2
• CMake - Cross-platform family of tools designed to build, package and test software. Written in C++11. BSD 3-Clause
• GNU Make - Tool which controls the generation of executables and other non-source files of a program. GPL 3
• jamplus/jamplus - Jamplus is a generic code and data build system derived from the original Perforce version of Jam. License
• Libtool - Generic library support script. Part of the Autotools. GPL 2
• Meson - Build system based on Ninja and Python. Apache 2
• ninja-build/ninja - Small, simple build system with a focus on speed. Apache 2
• Premake - Generates project files for Visual Studio, Xcode and GNU Make. Targets suppport can be extended via modules. BSD 3-Clause
• Qbs - Modern build tool for software projects. Licenses
• qmake - Build system included with the Qt Framework. Licenses
• SCons/scons - Software construction tool based on Python. License
• gittup/tup - Tup is a file-based build system. GPL 2
• xmake-io/xmake - Cross-platform build utility based on Lua. Apache 2
• zeromq/zproject - Project generator and build system support tool for ZeroMQ project. MPL 2
• michaelforney/samurai - ninja-compatible build tool written in C. Licenses
• matricks/bam - Build system with Lua scripting. License

^ Compilers

• rui314/8cc - A Small C Compiler. MIT
• rui314/9cc - A Small C Compiler. MIT
• jserv/amacc - Small C Compiler generating ELF executable for Arm architecture. GPL 2
• andrewchambers/c - small self hosting C compiler. BSD 2-Clause
• cc65/cc65 - cc65 - a freeware C compiler for 6502 based systems. Zlib
• Clang - Compiler for LLVM. Supports C11. NCSA
• CompCert - Fully-verified C compiler. Supports almost all of C89. License
• GCC a C compiler as part of its compiler set. Supports C11. License
• Intel SPMD - Compiler for a variant of the C language, for single program, multiple data programming. License
• PCC - Venerable compiler. Supports C99. Licenses
• larmel/lacc - A simple, self-hosting C compiler. MIT
• drh/lcc - The lcc retargetable ANSI C compiler. License
• TCC - Tiny C Compiler; a small, fast C compiler. Supports C99 (except complex types). LGPL 2.1
• alexfru/SmallerC - Simple C compiler. License
• michaelforney/cproc - C11 compiler for unix-like systems. License

^ Debugging and Analysis

• C-Reduce - Tool that takes a large C file with a property of interest and automatically produces a much smaller C file that has the same property. Intended to help create minimal bug-demonstrating cases in complex code. License
• CBMC - C Bounded Model Checker; a tool for verification of array bounds, pointer safety and user-specified assertions. License
• cgdb/cgdb - Console front-end to the GNU debugger. GPL 2
• GNU cflow - Analyzes a collection of source files and prints a graph charting control flow in the program. GPL 3
• ClangCheck - Static analysis tool, designed to work with Clang. NCSA
• GNU Complexity - Tool for measuring the complexity of source code. GPL 3
• Cppcheck - Static analysis tool. Despite the name, works well with C. GPL 3
• CScout - Source code analyzer and refactoring browser for C programs. GPL 3
• agl/ctgrind - Checking that functions are constant time with Valgrind. No license
• GNU DDD - Graphical front-end for a range of command-line debuggers. Licenses
• GDB - GNU Project debugger. Licenses
• lldb - LLVM debugger. NCSA
• rr - Debugger that records non-deterministic executions to allow for deterministic debugging. License
• SVF-tools/SVF - Pointer Analysis and Program Dependence Analysis for C and C++ Programs. License
• Valgrind - Range of dynamic analysis tools, including a leak checker. GPL 2

^ Documentation Generation

• Cxref - Generates documentation in either LaTeX, HTML, RTF or SGML. GPL 2
• DocOnce - Modestly tagged markup language that can be used to generate a range of formats. BSD 3-Clause
• Doxygen - De-facto standard tool for generating documentation from annotated sources. Can generate a large range of formats. GPL 2
• GTK-Doc - Tool for generating C documentation from annotated sources. Has support for the Autotools. GPL 2

^ Editors

• Anjuta DevStudio - GNOME IDE. GPL 2
• Atom - Hackable text editor for the 21st century. MIT
• Code::Blocks - Extendable, configurable IDE supporting C. GPL 3
• CodeLite - Cross-platform IDE. GPL 2
• Eclipse - IDE written in Java. EPL 2
• Geany - Small and fast IDE. GPL 2
• KDevelop - KDE IDE. GPL 2
• Qt Creator - Cross-platform IDE written with C++ and Qt, part of the Qt SDK. Supports Clang Code Model. GPL 3 w/ exceptions
• Visual Studio Code - Code editing, redefined. Visual Studio Code. MIT

^ Microsoft Windows Environment

• Cygwin - Designed to emulate a POSIX-compatible environment extensively under Windows. Licenses
• MinGW-w64 - Minimalist environment for C development on Windows with 64 bit support. Licenses
• MSYS2 - Minimal SYStem 2; aims to provide support for a POSIX environment on Windows, with a package manager based on Arch Linux's pacman. Packages have individual licenses, otherwise, as MinGW and Cygwin. BSD 3-Clause
• reactos - A free Windows-compatible Operating System. GPL 2

^ Profiling

• gperftools - Collection of utilities for measuring and improving performance. BSD 3-Clause
• gprof - Performance analysis tool. Part of GNU binutils. Licenses
• OProfile - Statistical profiler for Linux. Can profile any code (including the kernel!) with low overhead and without recompilation. GPL 2
• perf - Linux kernel-based profiler with a lot of functionality. GPL 2

^ Text Editor Extensions

• CCompletion - Notepad++ autocompletion plugin. Works with all identifiers recognized by Ctags. This is a download link. [GPL 2]
• CEDET - Collection of Emacs Development Environment Tools; designed to provide IDE-like features to Emacs. Built-in. GPL 2
• lvzixun/Clang-Complete - an autocomplete plugin for sublimetext3. No license
• editorconfig-core-c - EditorConfig core library written in C (for use by plugins supporting EditorConfig parsing). License
• Flycheck - Modern syntax checking for Emacs. For C, it can use either GCC or Clang as a back-end. GPL 3
• AtomLinter/linter-clang - Lint C code in Atom, using Clang. No license
• hebaishi/linter-gcc - Lint C code in Atom, using GCC. MIT
• Neomake - make and linting framework for Neovim/Vim. MIT
• Syntastic - Syntax checking and linting for Vim. WTFPL
• YASnippet - Emacs code template system, with C templates for common snippets. EPLA
• YouCompleteMe - Code completion engine for Vim. GPL 3

^ Utilities

• Artistic Style - Fast and small automatic source code formatter that supports C. MIT
• biicode - Dependency manager. MIT
• ryanmjacobs/c - Compile and execute C "scripts" in one go on the command line. Also has shebang support. MIT
• libav/c99-to-c89 - Tool to convert C99 code to MSVC-compatible C89. Apache 2
• RhysU/c99sh - Run C files using hash-bang. BSD 2-Clause
• aquynh/capstone - Dissasembly/disassembler framework. BSD 3-clause
• ccache - Compiler cache designed to speed up recompilation. GPL 3
• cdecl - Online service to translate C declarations into English and vice versa. [Public domain]
• cinclude2dot - Graphs include dependencies in a project using Graphviz. GPL
• jbremer/darm - A light-weight and efficient disassembler written in C for the ARMv7 instruction set. BSD 3-Clause
• jacob-carlborg/dstep - A tool for converting C and Objective-C headers to D modules. Boost
• anael-seghezzi/CToy - Interactive C coding environment. License
• distcc - Program that allows builds to be distributed among several machines. GPL 3
• GNU Global - Source code tagging tool. GPL 3
• GPP - General-purpose preprocessor. More versatile than the C preprocessor, but more flexible than m4. LGPL 3
• Highlight - Converts source code to formatted text with highlighting. GPL 3
• include-what-you-use - Helps find unecessary inclusions and make suggestions for fixing them. Based on LLVM/Clang (and only works with it). License
• GNU indent - Formats C source code automatically to make it easier to read. Also converts from one style of source to another. GPL 3
• m-schmoock/lcpp - A Lua C PreProcessor. MIT
• mcpp - Portable C preprocessor. 2-clause BSD
• jimenezrick/patch-AuthenticAMD - Utility for patching binaries generated by the Intel Compiler to get the maximum performance on AMD CPUs. GPL 3
• radare2 - unix-like reverse engineering framework and commandline tools security. LGPL 3
• buserror/simavr - simavr is a lean, mean and hackable AVR simulator for linux & OSX. GPL 3
• SMACK - Modular software verification toolchain and a self-contained software verifier. Currently only works with programs compiled using Clang. License
• sickill/stderred - stderr in red. License
• ggreer/the_silver_searcher - A code-searching tool similar to ack, but faster. Apache 2
• unifdef - Removes #ifdef and #if directives with their delimited text without touching any other part of the file. Licenses

^ Books

Reference Books

• C in a Nushell 2E - Concise reference book for C11.
• C Pocket Reference - Concise reference book for C99.
• C: A Reference Manual 5E - Full reference book for C99.
• SEI CERT C Coding Standard - Coding recommendations from CERT.
• The C Programming Language 2E - Original book on C, by its creators.

Beginner Books

• C Primer Plus 6E - Complete tutorial on programming in C11.
• C Programming: A Modern Approach - Book to learn the basics of C.
• Head First C - 'Head-first' style book for learning C.
• The GNU C Programming Tutorial - Beware, GNU C is not standard C. (PDF)

Intermediate Books

• 21st Century C - Programming book on C that touches tooling subject.
• Understanding and Using C Pointers - In-depth book on pointers in C.
• Algorithms in C, Parts 1-4: Fundamentals, Data Structures, Sorting, Searching
• C Interfaces and Implementations: Techniques for Creating Reusable Software
• The Standard C Library
• Let Us C
• C Programming FAQs: Frequently Asked Questions
• OpenGL SuperBible
• OpenGL Insights
• Effective C: An Introduction to Professional C Programming

Advanced Books

• Expert C Programming: Deep C Secrets - Interesting, in-depth and entertaining look at the innards of C.
• Pointers on C
• The C Puzzle Book

^ Benchmarks

• Benchmarks of the Lockless Memory Allocator
• Comparison of C/POSIX standard library implementations for Linux - A bit outdated, but shows overall tendencies
• Finding the best 64-bit simulation PRNG
• rxin/db-benchmarks - Collection of some database benchmarks, along with tools to parallelize the data generation.

^ Beginner Level

• A tutorial on pointers
• A tutorial on portable Makefiles
• Building C Projects
• Introduction to `fun' C
• Learning C with GDB
• Tutorial on pointers
• C Programming Wikibook
• POSIX Threads Programming tutorial
• Templating in C

^ Intermediate Level

• A comprehensive MPI tutorial resource
• Diving into concurrency: trying out mutexes and atomics
• Generic C reference counting
• How to write portable C without complicating your build
• Scalable C - Writing Large-Scale Distributed C
• 8 gdb tricks you should know
• 10 C99 tricks
• Introduction to OpenMP (video)
• OpenMP tutorial
• memcpy vs memmove
• MPI tutorial
• Some unknown features or tricks in C language
• The lost art of C structure packing
• What a C programmer should know about memory
• What every C programmer should know about undefined behaviour
• arjun024/hide-data-in-ptr - how to hide data inside pointers
• OpenGL Book
• Autotools Tutorial (PDF)
• C FAQ - comp.lang.c Frequently Asked Questions
• Akagi201/learning-cmake - CMake examples
• Let's build a database
• nikhilm/uvbook - An Introduction to libuv
• The ``Clockwise/Spiral Rule''

^ Advanced Level

• Advanced metaprogramming in C
• Quick tutorial on implementing and debugging malloc, free, calloc, and realloc
• Bit twiddling hacks
• I do not know C
• Implementing smart pointers for the C programming language
• Inline functions in C
• Metaprogramming custom control structures in C
• Some dark corners of C (Presentation)
• Writing efficient C and C code optimization
• What every programmer should know about memory (PDF)
• Learn libuv
• Let's build a compiler
• Write a compiler

^ Operating Systems

• Plan 9 - OS from Bell Labs.
• ChibiOS - RTOS with development environment.
• EtchedPixels/FUZIX - Superior rehaul of UZI.
• Harvey-OS/harvey - An OS based on Plan 9.
• SilverRainZ/OS67 - An Unix-like toy kernel.
• RIOT-OS/RIOT - OS for IoT.
• arjun024/mkernel - Very basic kernel.
• Stichting-MINIX-Research-Foundation/minix - MINIX3.
• guilleiguaran/xv6 - Mirror for Xv6 operating system.
• raphydaphy/Q-Operating-System - Ambitious and abandoned OS designed for 64-bit CPUs.
• seL4/seL4 - Microkernel aimed to be secure and correct.
• klange/toaruos - Desktop OS with userspace, written from scratch.
• nickbjohnson4224/rhombus - OS with libc and some drivers ready.
• rswier/swieros - Kernel, compiler and userland.
• jbangert/trapcc - Example of using Intel instruction execution gimick.
• mbedmicro/mbed - OS for ARM Cortex-M.

^ Emulators, VMs

• CTurt/Cinoop - Multiplatform Game Boy emulator.
• LIJI32/SameBoy - Game Boy and Game Boy Color emulator written in C.
• MoarVM - A VM with adaptive optimization and JIT compilation, built for Rakudo Perl 6.
• felixangell/mac - Virtual machine in c.
• jakogut/tinyvm - TinyVM is a small, fast, lightweight virtual machine written in pure ANSI C.
• rsms/sol - A sunny little virtual machine.
• mgba - mGBA Game Boy Advance Emulator.
• tekknolagi/carp - Well documented VM written from scratch.
• reicast/reicast-emulator - Multiplatform Sega Dreamcast emulator.
• haldean/x6502 - 6502 emulator that one day dreams of being an Atari 2600.
• n64dev/cen64 - Cycle-Accurate Nintendo 64 Emulator.
• wkoszek/cpu60 - Example of CPU simulation in software.
• swetland/dcpu16 - Virtual Machine and Assembler for Notch's DCPU-16 Architecture.
• AlexAltea/orbital - PS4 emulator.
• superzazu/8080 - Intel 8080 emulator.

^ UI, Windowing, Graphics

• LemonBoy/bar - A featherweight bar based on xcb.
• HarveyHunt/howm - A lightweight, X11 tiling window manager that behaves like vim.
• chneukirchen/cwm - portable version of OpenBSD's cwm(1) window manager.
• mil/foo-wm - A minimal window manager that organizes windows in a tree data structure, provides a socket to send commands to, and nothing more.
• pyknite/catwm - catwm is a very simple tiling window manager.
• jordansissel/xdotool - fake keyboard/mouse input, window management, and more.
• muennich/sxiv - Simple X Image Viewer.
• island-org/island - Lightweight and low-level creative coding toolkits in C.
• robm/dzen - Dzen is a general purpose messaging, notification and menuing program for X11.
• McNopper/OpenGL - OpenGL 3 and 4 with GLSL.
• superjer/tinyc.games - Tiny C games you can compile and run.
• DanteFalzone0/physics - An simple, interactive physics simulation.

^ Language Implementations

• Fedjmike/mini-c - Dr Strangehack, or: how to write a self-hosting C compiler in 10 hours.
• HuoLanguage/huo - Interpreted language written in C.
• Wilfred/babyc - A toy C compiler.
• dimkr/szl - A lightweight, embeddable scripting language.
• espruino/Espruino - The Espruino JavaScript interpreter.
• fabianishere/brainfuck - Brainfuck interpreter written in C.
• feeley/gambit - Gambit is an efficient implementation of the Scheme programming language.
• wren-lang/wren - The Wren Programming Language.
• cksystemsteaching/selfie - An educational software system of a tiny self-compiling C compiler, a tiny self-executing RISC-V emulator, and a tiny self-hosting RISC-V hypervisor.
• darius/ichbins - A tiny self-hosting Lisp-to-C compiler.
• fragglet/yoctolisp - Tiny Scheme-like Lisp interpreter written in a weekend.
• marcobambini/gravity - Gravity Programming Language.
• justinmeza/lci - A LOLCODE interpreter written in C.
• mruby/mruby - Lightweight Ruby.
• stevedekorte/io - Io programming language.
• philburk/pforth - Portable Forth in C.
• carld/micro-lisp - A very small Lisp programming language that used to be under 200 lines of C.
• kevinlawler/kona - Open-source implementation of the K programming language.
• ndreynolds/flathead - A toy JavaScript interpreter written in C.
• bl0ckeduser/new-bpf-tools - Subset-of-C compiler targeting 32-bit x86.
• intellectualheaven/ceed - A tiny x86 compiler with ELF and PE target.
• janet-lang/janet - A dynamic language and bytecode vm.
• jnz/q3vm - Q3VM - Embeddable bytecode virtual machine/interpreter for C-language input.
• tj/luna - luna programming language - a small, elegant VM implemented in C.
• rui314/minilisp - A readable lisp in less than 1k lines of C.
• rebol/rebol - Source code for the Rebol interpreter.
• mortdeus/legacy-cc - The earliest versions of the very first c compiler known to exist in the wild written by the late legend himself dmr.
• paladin-t/my_basic - Lightweight BASIC interpreter written in standard C in dual files. Aimed to be embeddable, extendable and portable.
• pikelang/Pike - Pike is a dynamic programming language with a syntax similar to Java and C. It is simple to learn, does not require long compilation passes and has powerful built-in data types allowing simple and really fast data manipulation.
• riolet/rix - Rix language combines the power of C language and the convenience of a high level language.
• lotabout/write-a-C-interpreter - Write a simple interpreter of C. Inspired by c4 and largely based on it.
• nickdesaulniers/bf_interpreter_jit_compiler - Teach myself about interpreters, JITs, and compilers using the Brainfuck language as the toy language.
• skx/simple.vm - Simple virtual machine which inteprets bytecode.

^ Challenges

• trailofbits/cb-multios - DARPA Challenges Sets for Linux, Windows, and macOS.
• FreddieV4/DailyProgrammerChallenges - External Repo of Challenges from r/dailyprogrammer.
• Coderbyte challenges
• Project Euler
• HackerRank
• CodeChef
• CodeWars
• Codingame
• /r/DailyProgrammer
• leetcode
• eatnumber1/goal - g()()()()('al') → "gooooal"

^ Other Examples

• MinhasKamal/CreepyCodeCollection - A Nonsense Collection of Disgusting Codes.
• Visgean/Zeus - Zeus trojan horse - leaked in 2011.
• andreafabrizi/prism - PRISM is an user space stealth reverse shell backdoor, written in pure C.
• brenns10/lsh - Simple shell implementation.
• jeff-1amstudios/restful-doom - HTTP+JSON API hosted inside the 1993 DOOM engine!
• chelyaev/ffmpeg-tutorial - A set of tutorials that demonstrates how to write a video player based on FFmpeg.
• rcr/rirc - A terminal IRC client in C.
• xoreaxeaxeax/movfuscator - The single instruction C compiler.
• deadbits/InsecureProgramming - Mirror of insecure programming examples.
• irssi/irssi - The client of the future.
• xorg62/tty-clock - Clock using lib ncurses.
• vanhauser-thc/thc-hydra - Hydra.
• posva/catimg - Fast image printing in your terminal.
• pkieltyka/stash - Steganography application that hides data within a bitmap image.
• regehr/ub-canaries - Collection of C/C++ programs that try to get compilers to exploit undefined behavior.
• tnightingale/DTE - Dumb Terminal Emulator - Data Comm, COMP 3980.

^ AI

Neural nets, machine learning, pattern recognition etc.

• cjac/cmusphinx - CMU Sphinx - Speech Recognition Toolkit. Licenses
• 100/Cranium - A portable, header-only, artificial neural network library written in C99. MIT
• pjreddie/darknet - Convolutional Neural Networks. License
• TheWeatherChannel/dClass - Device Classification Engine. Apache 2
• 2hanson/DecisionTree - Decision Tree. MIT
• yusugomori/DeepLearning - Deep Learning (several languages, C included). MIT
• encog/encog-c - C implementation of Encog - machine learning framework for Java/C#. No license
• codeplea/genann - simple neural network library in ANSI C. Zlib
• attractivechaos/kann - Two-file ANN library. MIT
• Blei-Lab/lda-c - This is a C implementation of variational EM for latent Dirichlet allocation (LDA), a topic model for text or other discrete data. LGPL 2.1
• jppbsi/LibDEEP - Deep learning library. No license
• H2CO3/libsprec - C library for speech recognition using the Google Speech API. License
• robwhess/opensift - Open-Source SIFT Library. License
• dake/openVP - Voice Print Recognition in C language. No license
• cmusphinx/pocketsphinx - Lightweight speech recognition engine, specifically tuned for handheld and mobile devices, though it works equally well on the desktop. BSD 2-Clause
• HIPS/Probabilistic-Backpropagation - Implementation in C and Theano of the method Probabilistic Backpropagation for scalable Bayesian inference in deep neural networks. BSD 3-Clause
• GHamrouni/Recommender - A C library for product recommendations/suggestions using collaborative filtering (CF). BSD 2-Clause
• ufoym/recursive-bf - A lightweight library for recursive bilateral filtering. MIT
• xiph/rnnoise - Recurrent neural network for audio noise reduction. License
• antirez/shapeme - Evolve images using simulated annealing. BSD 2-Clause
• symisc/sod - An Embedded Computer Vision & Machine Learning Library (CPU Optimized & IoT Capable). GPL 3
• iunderstand/SWE - Learning Semantic Word Embeddings based on Ordinal Knowledge Constraints. Apache 2
• glouw/tinn - The tiny neural network library. MIT
• canyalniz/CNN-Inference-Didactic - A readable CNN Inference implementation in C. GPL 3

^ Algoritm Implementations

Some generic agoritms or ones with no specific attachments.

• dhuertas/AES - AES algorithm implementation in C. No license
• mischasan/aho-corasick - A-C implementation in "C". Tight-packed (interleaved) state-transition matrix. LGPL 3
• davidreynolds/algorithms - A repository of assorted algorithms and data structures. No license
• BigZaphod/AStar - C Implementation of the A* Pathfinding Algorithm. License
• citiususc/BigBWA - Approaching the Burrows-Wheeler Aligner to Big Data Technologies. GPL 3
• TheAlgorithms/C - All Algorithms implemented in C No license
• chaoslawful/ccard-lib - C library for estimating cardinality in streams for which it is infeasible to store all events in memory. No license
• agl/curve25519-donna - Implementations of a fast Elliptic-curve Diffie-Hellman primitive. License
• aimxhaisse/des - C implementation of DES. License
• tarequeh/DES - Implementation of Data Encryption Standard in C. MIT
• blynn/dlx - Implementation of Knuth's Algorithm X, with example solvers. GPL 3
• oap/ekf-angles - Extended Kalman Filter for Accelerometer and Gyro data. No license
• Cyan4973/FiniteStateEntropy - Finite State Entropy and Huff0. BSD 2-Clause
• BlackLight/fkmeans - A tiny library in C for managing kmeans clusterization algorithm over arbitrary data sets, both by manually specifying the number k of clusters and computing it automatically using Schwarz criterion. GPL 3
• kljensen/Gemoda - A generic motif discovery algorithm for sequential data. GPL 2
• lacker/ikalman - An iPhone-friendly Kalman filter written in C. MIT
• tsuraan/Jerasure - C Implementation of Reed-Solomon coding. License
• jmcejuela/Levenshtein-MySQL-UDF - General Levenshtein algorithm and k-bounded levenshtein distance in linear time and constant space. LGPL 3
• CVLearner/Mixture-of-Gaussians - Fit a Gaussian mixture model given a set of data. MIT
• richarddurbin/pbwt - Implementation of Positional Burrows-Wheeler Transform for genetic data. License
• ntamas/plfit - Fitting power-law distributions to empirical data, according to the method of Clauset, Shalizi and Newman. License
• Kevincav/Radix-Sort - Radix Sort with different data types. MIT
• duckythescientist/obfuscatedLife - Conway's Game of Life in 9 lines of C. No license
• kokke/tiny-AES-c - Small portable AES128/192/256 in C. Unlicense
• kroitor/gjk.c - Gilbert-Johnson-Keerthi (GJK) collision detection algorithm in 200 lines of clean plain C. WTFPL
• ai-ku/scode - Sphere embedding (s-code) is a variation of Euclidean embedding of co-occurence data (code). MIT
• swenson/sort - Collection of sorting routines, which type-specialize at compile-time with a user-defined type. MIT
• msteinbeck/tinyspline - ANSI C library for NURBS, B-Splines, and Bézier curves with interfaces for C++, C#, D, Java, Lua, Octave, PHP, Python, R, and Ruby. MIT
• ferreiradaselva/uastar - Minimal A* implementation. Zlib
• madler/crcany - CRC calculation library. Zlib

^ Argument Parsing

• cofyc/argparse - Command-line arguments parsing library. MIT
• clibs/commander - Commander option parser ported to C - simple API, auto-generated --help. MIT
• docopt/docopt.c - Implementation of a command-line option parser. MIT
• clibs/flag - Go-style flag parsing for C. MIT
• jibsen/parg - A single-file reimplementation of getopt with better defaults. License

^ Calculations and Math

• b-k/apophenia - Library for statistical and scientific computing. GPL 2
• fredrik-johansson/arb - Library for arbitrary-precision interval arithmetic. LGPL 2.1
• ATLAS - Automatically Tuned Linear Algebra Software. License
• BLAS - Basic Linear Algebra Subprograms; a set of routines that provide vector and matrix operations. License
• Lichtso/CCWT - Complex Continuous Wavelet Transformation. MIT
• CDFLIB - Library with routines to evaluate cumulative density functions for a variety of standard probability distributions. Also can compute one parameter of the CDF given the others. No license
• ScientificC/cmathl - Pure-C Math library with a great variety of mathematical functions and CMake build support. Seeks to be close to C89/C90 compliant for portability. MIT
• Cuba - Library for multidimensional numerical integration. LGPL
• adis300/fft-c - A high-performance Fourier Transform from netlib's fftpack; wrapped in a user-friendly format. MIT
• FFTW - The Fastest Fourier Transform in the West; a highly-optimized fast Fourier transform routine. GPL 2
• FLINT - Fast Library for Number Theory; a library supporting arithmetic with numbers, polynomials, power series and matrices, among others. LGPL 2.1
• gjrand - Library of random-number generation routines. GPL 2
• GLPK - GNU Linear Programming Kit; a package designed for solving large-scale linear programming, mixed integer programming and other related problems. GPL 3
• GMP - GNU Multple Precision Arithmetic Library; a library for arbitrary-precision arithmetic. Licenses
• GNU MPC - Library for complex number arithmetic. LGPL 3
• GNU MPFR - Library for arbitrary-precision floating-point arithmetic. LGPL 3
• GNU MPRIA - Portable mathematics library for multi-precision rational interval arithmetic. GPL 3
• GSL - The GNU Scientific Library; a sophisticated numerical library. GPL3
• HdrHistogram/HdrHistogram_c - C port of the HdrHistogram. License
• igraph- Library for creating and manipulating large graphs. GPL2
• KISS FFT - Very simple fast Fourier transform library. BSD
• LAPACKE - C interface to LAPACK. License
• PARI/GP - Computer algebra system for number theory; includes a compiler to C. GLP
• PETSc - Suite of data structures and routines for scalable parallel solution of scientific applications modelled by partial differential equations. License
• PROB - Library that handles various discrete and continuous probability density functions. LGPL 3
• PetteriAimonen/libfixmatrix - C library for fixed point matrix, quaternion and vector calculations. MIT
• canonizer/libgpuvm - library which simplifies host-GPU data transfer using userspace pagefault handling. No license
• libtom/libtommath - LibTomMath is a free open source portable number theoretic multiple-precision integer library written entirely in C. Unlicense
• JuliaMath/openlibm - High quality system independent, portable, open source libm implementation. License
• imneme/pcg-c - PCG — C Implementation. Apache 2
• imneme/pcg-c-basic - PCG — Minimal C Implementation. Apache 2
• libtom/tomsfastmath - TomsFastMath is a fast public domain, open source, large integer arithmetic library written in portable ISO C. Licenses
• cvxgrp/scs - C package that solves convex cone problems via operator splitting. MIT
• SLEPc - Library for the solution of large, sparse eigenvalue problems on parallel computers. BSD 2-Clause
• slim-curve/slim-curve - SLIM Curve: a package for exponential curve fitting of combined spectral lifetime image data. GPL 3
• tinyexpr - Tiny recursive-descent parser, compiler and evaluation engine for simple mathematical expressions. Zlib
• Yeppp! - Very fast, SIMD-optimized mathematical library. License
• PetteriAimonen/libfixmath - Cross Platform Fixed Point Maths Library.MIT
• datenwolf/linmath.h - Linear math as required for computer graphics. WTFPL

^ Compression

• Blosc/bcolz - Fast, multi-threaded, meta-compressor library. Licenses
• kiyo-masui/bitshuffle - Filter for improving compression of typed binary data. License
• google/brotli - Generic lossless compression algorithm based on LZ77, Huffman coding and 2nd order context modelling. MIT
• bzip2 - Patent-free, high-quality data compression library. BSD 4-Clause
• Blosc/c-blosc - A blocking, shuffling and loss-less compression library that can be faster than memcpy(). Licenses
• clzip - C lzip implementation. GPL 2
• richox/comprox - An experimental lossless data compression program with high compression ratio. BSD 3-Clause
• RoaringBitmap/CRoaring - Roaring bitmaps in C (and C++). Apache 2
• adnanozsoy/CUDA_Compression - A GPU-based LZSS compression algorithm, highly tuned for NVIDIA GPGPUs and for streaming data, leveraging the respective strengths of CPUs and GPUs together. Apache 2
• centaurean/density - Superfast compression library. BSD 3-Clause
• gildor2/fast_zlib - Improved zlib, which runs 2 to 10 times faster. BSD 3-Clause
• Cyan4973/FiniteStateEntropy - Two efficient compression codecs optimized for modern CPUs. BSD 2-Clause
• rjsikarwar/gpu_compression - Nine Light weight Schemes to Compress and Decompress the data of Database Using GPU and also a planer. No license
• atomicobject/heatshrink - data compression library for embedded/real-time systems. ISC
• adamierymenko/huffandpuff - Minimal Huffman encoder and decoder. Public domain
• libarchive/libarchive - Multi-format archive and compression library. Licenses
• nih-at/libzip - A C library for reading, creating, and modifying zip archives. BSD 3-Clause
• inikep/lizard - Formerly LZ5. Achieves compression ratios comparable with zip and zlib at decompression speeds of 1000MB/s and faster. Licenses
• lz4/lz4 - Extremely Fast Compression algorithm. Licenses
• lzo - Very fast data compression library. GPL 2
• richgel999/miniz - Single C source file zlib-replacement library. License
• moinakg/pcompress - A Parallelized Data Deduplication and Compression utility. LGPL 3
• vasi/pixz - Parallel, indexed xz compressor. BSD 2-Clause
• mist64/pucrunch - pucrunch, an Optimizing Hybrid LZ77 RLE Data Compression Program for C64/C128/VIC-20/Plus4. LGPL 2.1
• quicklz - Fast compression library. Licenses
• Ed-von-Schleck/shoco - Compressor for small text strings. MIT
• lemire/simdcomp - Simple library for compressing lists of integers using binary packing. Makes use of SIMD instructions on x86. BSD 3-Clause
• antirez/smaz - Small strings compression library. BSD 3-Clause
• andikleen/snappy-c - C port of the snappy compressor. License
• quixdb/squash - Compression abstraction library, complete with utilities. MIT
• powturbo/TurboPFor - Fast integer compression. GPL 2
• powturbo/TurboRLE - Fastest Run Length Encoding. GPL 2
• kuba--/zip - A portable, simple zip library written in C. Unlicense
• madler/zlib - Massively-spiffy yet delicately-unobtrusive compression library. Zlib
• zlib-ng/zlib-ng - zlib replacement with optimizations for "next generation" systems. Zlib
• facebook/zstd - Fast real-time compression algorithm. BSD 3-Clause
• jsvennevid/filearchive - File archive library allowing for easy creation and access to data stored inside a container through a simple API. MIT
• ariya/FastLZ - Byte-aligned LZ77 compression. License

^ Concurrency and Parallelism

• yosefk/checkedthreads - A simple library for parallelism, with built-in checking for race conditions. BSD 2-Clause
• FCFS RWLock - First-come first-served Readers/Writers lock for POSIX threads. Licenses
• sharow/libconcurrent - Concurrent programming library, using coroutines, for C11. Zlib
• liburcu - Data synchronization library, which scales linearly with the number of cores. LGPL 2.1
• cchan - Small library for channel constructs for inter-thread communication. Public Domain
• pmodels/mpich - Another implementation of MPI. License
• open-mpi/ompi - Message passing interface implementation. License
• GNU pth - Portable implementation for non-preemptive priority-based scheduling for multiple threads of execution. LGPL 2.1
• POSIX threads - The POSIX thread library. No license
• tinycthread/tinycthread - Portable, small implementation of the C11 threads API. License
• Pithikos/C-Thread-Pool - A minimal but powerful thread pool in ANSI C. MIT
• baruch/libwire - User space threading (aka coroutines) library for C resembling GoLang and goroutines. MIT
• bjoernknafla/amp - C portable low-level assemblies for parallelism and threading. BSD 3-Clause
• bjoernknafla/peak - Parallelism exploration assembly kit. C toolkit to experiment with task- and data-parallelism. BSD 3-Clause
• cloudwu/coroutine - A asymmetric coroutine library for C. MIT
• concurrencykit/ck - Concurrency primitives, safe memory reclamation mechanisms and non-blocking (including lock-free) data structures designed to aid in the research, design and implementation of high performance concurrent systems developed in C99+. Licenses
• etmc/lemon - Lemon is an MPI parallel I/O library that is intended to allow for efficient parallel I/O of both binary and metadata on massively parallel architectures. Data is stored in the SciDAC Lattice QCD Interchange Message Encapsulation format, that allows for storing large blocks of binary data and corresponding metadata in the same file. GPL 3
• geertj/cgreenlet - Coroutines for C/C++. MIT
• halayli/lthread - lthread, a multicore enabled coroutine library written in C. BSD 2-Clause
• hnes/libaco - A blazing fast and lightweight C asymmetric coroutine library. Apache 2
• jtsiomb/c11threads - Trivial C11 threads.h implementation over POSIX threads. Public domain
• matianfu/FUNK - a c continuation library inspired by Adam Dunkel's ProtoThread. Apache 2
• mbrossard/threadpool - A simple C Thread pool implementation. BSD 2-Clause
• oneoo/alilua-coevent-module - epoll base coroutine module. MIT
• ramonza/libcoro - Lightweight C coroutines. BSD 2-Clause
• sustrik/libdill - Structured concurrency in C. MIT
• sustrik/libmill - Go-style concurrency in C. MIT
• stevedekorte/coroutine - C multiplatform coroutine implementation via ucontext, fibers or setjmp. No license
• parallella/pal - An optimized C library for math, parallel processing and data movement. Apache 2
• danluu/setjmp-longjmp-ucontext-snippets - Implementing coroutines, channels, message passing, etc.Apache 2
• Precisamento/cpthreads - Cross Platform (e.g. Windows) support for C11 threads. MIT
• shiyanhui/libcsp - Concurrency C library influenced by the CSP model. MIT

^ Cryptography

• GNU SASL - Implementation of the Simple Authentication and Security Layer and few common SASL mechanisms. Licenses
• aidansteele/sphlib - Set of implementations of various hash functions, including several cryptographic ones. MIT
• GnuTLS - Secure communication library, implementing SSL, TLS and DTLS. LGPL 2.1
• libgcrypt - General-purpose cryptography library, with a range of available ciphers. Licenses
• OpenSSL - Implementation of the SSL and TLS protocols, and also includes a cryptography library. Licenses
• jedisct1/libsodium - A modern, portable and easy to use crypto library. ISC
• ARMmbed/mbedtls - An open source, portable, easy to use, readable and flexible SSL library. License
• B-Con/crypto-algorithms - Basic implementations of standard cryptography algorithms, like AES and SHA-1. No license
• WickrInc/wickr-crypto-c - An implementation of the Wickr Secure Messaging Protocol in C. License
• ashwinraghav/Parallel_Open_SSL - Use your idle GPU to encrypt your data. Give your CPU some breathing time! Licenses
• awslabs/s2n - s2n : an implementation of the TLS/SSL protocols. Apache 2
• bitcoin-core/secp256k1 - Optimized C library for EC operations on curve secp256k1. MIT
• cloudflare/keyless - CloudFlare's Keyless SSL Server Reference Implementation. Agreement
• ctz/cifra - A collection of cryptographic primitives targeted at embedded use. License
• cyassl/cyassl - Small, fast, portable implementation of TLS/SSL for embedded devices to the cloud. GPL 2
• eduardsui/tlse - Single C file TLS 1.2/1.3 implementation, using tomcrypt as crypto library. BSD 2-Clause
• h2o/picotls - TLS 1.3 implementation in C (master supports RFC8446 as well as draft-26, -27, -28). License
• jedisct1/libhydrogen - A lightweight, secure, easy-to-use crypto library suitable for constrained environments. ISC
• libressl-portable/openbsd - LibreSSL source code. Licenses
• libtom/libtomcrypt - LibTomCrypt is a fairly comprehensive, modular and portable cryptographic toolkit that provides developers with a vast array of well known published block ciphers, one-way hash functions, chaining modes, pseudo-random number generators, public key cryptography and a plethora of other routines. Licenses
• maciejczyzewski/retter - A collection of hash functions, ciphers, tools, libraries, and materials related to cryptography. No license
• mikeryan/crackle - Crack and decrypt BLE encryption. BSD 2-Clause
• open-quantum-safe/liboqs - C library for quantum-resistant cryptographic algorithms. MIT
• tbuktu/libntru - C Implementation of NTRUEncrypt. Licenses
• trezor/trezor-crypto - Heavily optimized cryptography algorithms for embedded devices. MIT
• droe/sslsplit - Transparent SSL/TLS interception. BSD 2-Clause
• orlp/ed25519 - Portable C implementation of Ed25519, a high-speed high-security public-key signature system. Zlib
• wolfSSL/wolfssl - wolfSSL (formerly CyaSSL) is a small, fast, portable implementation of TLS/SSL for embedded devices to the cloud. GPL 2
• rg3/bcrypt - bcrypt password hash C library. License
• LoupVaillant/Monocypher - An easy to use, easy to deploy crypto library. Licenses
• tombonner/blowfish-api - Blowfish block cipher implementation. License

^ Databases

• priitj/whitedb - Lightweight database library, operating entirely in main memory. GPL 3
• mongodb/mongo-c-driver - High-performance client library for MongoDB. Apache 2
• SQLite - Self-contained, serverless, zero-configuration, transactional SQL database engine with a C interface. Public domain
• symisc/unqlite - Self-contained, serverless, zero-configuration, transactional NoSQL engine with a C interface. License
• Akash91/CoSQL - A Co-Relational Key-Value Data Store. No license
• GNOME/libgda - Libgda is a (relatively small) database access library. GPL 2
• Softmotions/ejdb - EJDB — Embeddable JSON Database engine. MIT
• aerospike/aerospike-client-c - Aerospike C Client. License
• bcmpinc/dagdb - small database for storing semi-structured data. GPL 3
• maciejczyzewski/hashbase - A fast, efficient on-disk/in-memory database with many different kind of data structures. MIT
• maxmind/libmaxminddb - C library for the MaxMind DB file format. Apache 2
• pmwkaa/sophia - modern emeddable key-value database. License
• redis/hiredis - Minimalistic C client for Redis. BSD 3-Clause
• seppo0010/rlite - self-contained, serverless, zero-configuration, transactional redis-compatible database engine. rlite is to Redis what SQLite is to SQL. BSD 2-Clause
• sqlcipher/sqlcipher - SQLCipher is an SQLite extension that provides 256 bit AES encryption of database files. License
• tglman/orientdb-c - The C client of OrientDB. No license
• spotify/sparkey - Simple constant key/value storage library, for read-heavy systems with infrequent large bulk inserts. Apache 2
• vrogier/ocilib - Open source C and C++ library for accessing Oracle databases. Apache 2
• symisc/vedis - An Embedded Implementation of Redis. License
• orca-zhang/influxdb-c - C write client for InfluxDB. MIT
• t3rm1n4l/lightkv - Key-value data storage. No license

^ Data Structures and Types

• recp/ds - Common Data Structures and Algorithms. MIT
• P-p-H-d/mlib - Library for generic, but typesafe C containers. Implemented as header-only. BSD 2-Clause
• libsrt - Soft and hard real-time data structures. BSD 3-Clause
• nbulischeck/list.h - Implementations for single- and double-linked list functions. GPL 3
• gpakosz/PackedArray - Random-access array of tightly packed unsigned integers of any desired width. Has a SIMD-optimized implementation. WTFPL
• swenson/vector.h - Header library for typed lists. MIT
• 20centaurifux/datatypes - A collection of various datatypes in C (linked lists, stack, queue, red-black tree and hash table). GPL 3
• ClickerMonkey/CDSL - A data structure library written in C. License
• Incarnation-p-lee/libds - Unified data structure implementation library of C. GPL 2
• LPD-EPFL/ASCYLIB - Concurrent-search data-structure library with over 30 implementantions of linked lists, hash tables, skip lists, and binary search trees. GPL 2
• MichaelJWelsh/cdsa - A library of generic intrusive data structures and algorithms in ANSI C. ISC
• ZSShen/C-Common-Data-Structures - Uniform C APIs for data structure manipulation. No license
• agl/critbit - Critbit trees in C. No license
• antirez/rax - A radix tree implementation in ANSI C. BSD 2-Clause
• armon/libart - Adaptive Radix Trees implemented in C. BSD 3-Clause
• ashinkarov/trie - Simple implementation of trie data structure. License
• bcopeland/em_misc - External memory data structure playground. No license
• begeekmyfriend/bplustree - A minimal but extreme fast B+ tree indexing structure demo for billions of key-value storage. MIT
• chrismoos/hash-ring - C hash ring library. Apache 2
• chriso/bitset - A compressed bitset with supporting data structures and algorithms. LGPL
• codeprepper/data-structures - Arrays, linked lists, stacks and queues. MIT
• dminor/skip-quadtree - Implementation of the skip quadtree and compressed quadtree data structures. License
• douglascrockford/DEC64 - Decimal floating point. No license
• fmela/libdict - C library of key-value data structures with an object-oriented interface. BSD 2-Clause
• fragglet/c-algorithms - A library of common data structures and algorithms written in C. ISC
• gnudennis/ds_c - Data Structure In C. No license
• graphitemaster/libintrusive - Intrusive data structures for C. Unlicense
• grundprinzip/bitcompressedvector - Provide a container for integral data types that applies light-weight bit compression. License
• hacatu/haclib - A utility library providing data types C should have been made with such as vectors and sequences, mostly as macros. MPL 2
• hyPiRion/c-rrb - RRB-tree implemented as a library in C. MIT
• hyPiRion/roulette-tree - Data structure for efficient fitness-proportionate selection. MIT
• jarun/dslib - A library of handy data structures. GPL 3
• johnj/llds - Low-Level Data Structure - efficient data structures, and fast data access in the 2.6/3.0 kernel. License
• jtsiomb/kdtree - A simple C library for working with KD-Trees. License
• jvirkki/libbloom - A simple and small bloom filter implementation in plain C. BSD 2-Clause
• ksheedlo/kmdata - Data structures for C programmers, by C programmers. No license
• louiswins/RB-Tree - An implementation of the Red-Black Tree data structure. No license
• livioso/datastructures-in-C - Implementation of a some data structures in C for educational purposes. No license
• malbrain/Btree-source-code - A working project for High-concurrency B-tree source code in C. License
• michaeltyson/TPCircularBuffer - A simple, fast circular buffer implementation. License
• mikedlowis/data-structures - A collection of data structures implemented in C to be included in multiple projects. BSD 2-Clause
• naraing/dsLib - An algorithm library with core data-sttructures and common algortihm implementations on those data structures. GPL 3
• noporpoise/BitArray - C bit array structs and methods. License
• orangejulius/cs_fundamentals - simple implementations of common data structures/algorithms. GPL 3
• paulasmuth/libsmatrix - thread-safe sparse matrix data structure. MIT
• pcdavid/data-structures - Sample implementations of classical data structures in C. WTFPL
• petewarden/c_hashmap - A simple string hashmap in C. Public domain
• rxi/map - A type-safe hash map implementation for C. MIT
• rxi/vec - A type-safe dynamic array implementation for C. MIT
• siganakis/tny - Tiny data structures that pack a punch! License
• srdja/Collections-C - A library of generic data structures. LGPL 3
• steven-schronk/C-Data-Structures - Collection of basic data structures in C. GPL 3
• wasabiz/xrope - rope data structure. No license
• torch/tds - Torch C data structures. License
• watmough/jwHash - Simple hash table implementation for C. Apache 2
• zhemao/libds - Simple, memory-safe data-structures in C. MIT
• willemt/cbuffer - A circular buffer written in C using Posix calls to create a contiguously mapped memory space. License
• xant/libhl - Simple and fast C library implementing a thread-safe API to manage hash-tables, linked lists, lock-free ring buffers and queues. LGPL 3
• yuyuyu101/C-Buffered-tree - A buffered-tree implemented in dictionary type and more. MIT
• MagerValp/AsmHeap - Heap data structure in 6502 assembler. No license
• Snaipe/libcsptr - Smart pointers in C. MIT
• C-Macro-Collections - Generate simple and generic data structures using macros. MIT
• troydhanson/uthash - C macros for hash tables and more. License
• begeekmyfriend/CuckooFilter - Substitute for bloom filter. License
• bitly/dablooms - Scaling, counting, bloom filter library. MIT
• krglaws/KyleStructs - Simple data structures written for educational purposes. No license
• armon/c-minheap-array - Implements a Min-Heap / Priority Queue in C using a simple array. BSD 3-Clause
• jstimpfle/rb3ptr - Red-black tree in C. License

^ Events

• libev - Yet another event loop. BSD 2-Clause
• libevent - Event loop replacement for network servers. BSD 3-Clause
• Lupus/libevfibers - Small C fiber library that uses libev based event loop and libcoro based coroutine context switching. Apache 2
• facebook/libphenom - An eventing framework for building high performance and high scalability systems in C. Apache 2
• libuv/libuv - Cross-platform asychronous I/O. Licenses
• ithewei/libhv - Event-loop with non-blocking IO and timer. BSD 3-Clause

^ Foreign Function Interfaces

• GNU Libffcall - Collection of libraries for building foreign function interfaces. GPL 3
• dyncall - Another foreign function interface library. License
• atgreen/libffi - A portable foreign-function interface library. License
• dyu/ffi-overhead - comparing the c ffi overhead on various programming languages. Apache 2
• jmckaskill/luaffi - Standalone FFI library for calling C functions from lua. Compatible with the luajit FFI interface. License
• taviso/ctypes.sh - A foreign function interface for bash. MIT

^ Binaries

• bfd - Library for manipulating binary object files. Part of GNU binutils. Licenses
• 0intro/libelf - Simple library for parsing ELF files. MIT
• fuzxxl/memf - Portable scanf/printf-like functions to marshal binary data. BSD 2-Clause
• nicklockwood/FastCoding - A faster and more flexible binary file format replacement for NSCoding, Property Lists and JSON. License
• abiggerhammer/hammer - Parser combinators for binary formats. GPL 2

^ CSV

• rgamble/libcsv - Simple, streaming CSV parser. LGPL 2.1
• tadasv/csv_parser - Callback based (SAX like) CSV Parser for C. MIT

^ HTML

• lexborisov/Modest - Modest is a fast HTML renderer implemented as a pure C99 library with no outside dependencies. LGPL 2.1
• lexborisov/myhtml - Fast C/C++ HTML 5 Parser. Using threads. LGPL 2.1
• htacg/tidy-html5 - The granddaddy of HTML tools, with support for modern standards. License
• google/gumbo-parser - HTML5 parsing library in C99. Apache 2

^ JSON

• NeonMercury/jfes - JSON For Embedded Systems; simple JSON engine without any dependencies. MIT
• zserge/jsmn - Minimalistic JSON parser. MIT
• netmail-open/wjelement - Advanced JSON manipulation library, with support for JSON Schema. Licenses
• DaveGamble/cJSON - Ultralightweight JSON parser in ANSI C. MIT
• akheron/jansson - C library for encoding, decoding and manipulating JSON data. MIT
• armink/struct2json - A fast convert library between the JSON and C structure. Implement structure serialization and deserialization for C. MIT
• cesanta/frozen - JSON parser and generator for C/C++ with scanf/printf like interface. Targeting embedded systems. Apache 2
• cloudflare/lua-resty-json - JSON library for Lua and C. BSD 2-Clause
• json-c/json-c - Official code repository for json-c. License
• keenerd/jshon - JSON parser designed for maximum convenience within the shell. MIT
• kgabis/parson - Lightweight JSON library written in C. MIT
• kevinbirch/kanabo - Query JSON/YAML data with JSONPath. License
• lloyd/yajl - A fast streaming JSON parsing library in C. ISC
• orangeduck/json2c - Convert JSON to C data literals. BSD 3-Clause
• quartzjer/js0n - Flexible Zero-Footprint JSON Parser in C. Unlicense
• sheredom/json.h - JSON parser for C and C++. Unlicense
• vincenthz/libjson - JSON parser and printer library in C. Easy to integrate with any model. License
• udp/json-parser - Very low footprint JSON parser written in portable ANSI. License
• garnetius/jsong - Faster than light streaming JSON & USON parser and writer with rich and trivial to use API plus SSE optimizations. BSD 2-Clause
• recp/json - Parses JSON files into DOM-like data structures. MIT
• mjansson/json - Single header JSON/SJSON parser. Unlicense

^ INI

• ndevilla/iniparser - Parser for .ini files. MIT
• madmurphy/libconfini - Yet another INI parser. GPL 3
• benhoyt/inih - Simple .INI file parser in C, good for embedded systems. License
• LloydLabs/librini - Tiny, non-libc dependant, .ini file parser programmed from scratch in C99. MIT
• compuphase/minIni - A small and portable INI file library with read/write support. Apache 2

^ Markdown

• hoedown/hoedown - Fully standards-compliant, extension-supporting, UTF-8 aware, fast Markdown parser. ISC
• commonmark/cmark - Library for parsing the CommonMark dialect of Markdown. License
• Orc/discount- My C implementation of John Gruber's Markdown markup language. License
• commonsguy/cwac-anddown - CWAC AndDown: Markdown Utility Library. Apache 2
• fletcher/MultiMarkdown-6 - Lightweight markup processor to produce HTML, LaTeX, and more. License
• jgm/peg-markdown - An implementation of markdown in C, using a PEG grammar. Licenses
• vmg/sundown - Standards compliant, fast, secure markdown processing library in C. License

^ XML

• libexpat/libexpat - Stream-oriented XML parser. License
• libxml2 - Standards-compliant, portable XML parser. MIT
• michaelrsweet/mxml - Small XML reading and writing library. No dependencies aside from C standard library. Apache 2
• ooxi/xml.c - Simple XML subset parser comparable to glib's Markup parser. License
• bakulf/libmrss - C library for parsing, writing and creating RSS files or streams. LGPL 2.1
• mmuszkow/librss - RSS and ATOM parsing library. No license
• bakulf/libnxml - Library for parsing, writing and creating XML 1.0 and 1.1 documents. LGPL 2.1
• anton/rss_aggregator - Feed reader lib written in C with use of libxml2 and utlist. No license

^ Other Filetypes

• yaml/libyaml - Canonical source repository for LibYAML. MIT
• mongodb/libbson - BSON utility library. Apache 2
• martinh/libconfuse - Small configuration file parser library. ISC
• vstakhov/libucl - Universal configuration library parser. BSD 2-Clause
• Juniper/libxo - Allows an application to generate plain text, XML, JSON and HTML output using a common set of function calls. The application decides at runtime what output style should be produced. BSD 2-Clause
• brechtsanders/xlsxio - Cross-platform library for reading and writing .xlsx files. MIT
• arrbee/diff-match-patch-c - C language port of google-diff-match-patch library. License
• hyperrealm/libconfig - C/C++ library for processing configuration files. LGPL 2.1
• jedwing/CHMLib - Library for reading Microsoft ITSS/CHM format files. LGPL 2.1
• jmcnamara/libxlsxwriter - A C library for creating Excel XLSX files. License
• libharu/libharu - Free PDF library. Zlib
• samtools/htslib - C library for high-throughput sequencing data formats. License
• vmg/houdini - API for escaping text for the web. MIT
• trumpowen/MegaMimes - A C mime type library MIT

^ Flow Control and Language Extension

• orangeduck/Cello - Library introducing higher-level programming to C. BSD 2-Clause
• Ragel - DSL for state machines that compiles to C. License
• kitsune-dsu/kitsune-core - Efficient, general-purpose framework for dynamic software updating. License
• P99 - Suite of macros to implement advanced features like default function arguments, scope-bound resources, etc. License
• CObjectSystem/COS - C Object System. Apache 2
• H2CO3/Sparkling - Lightweight extension language. BSD 2-Clause
• lua/lua - Embeddable scripting programming language. License
• Zeex/subhook - Simple hooking library for C/C++ (x86 only, 32/64-bit, no dependencies). BSD 2-Clause
• arnaudbrejeon/cspec - Behavior driven development in C. GPL 3
• comex/substitute - A free runtime modification library. License
• elua/elua - Highly portable version of Lua. License
• eudoxia0/magma - Extending C with cmacro. License
• graphitemaster/lambdapp - Anonymous functions in C. Unlicense
• guillermocalvo/exceptions4c - Exception handling framework for C. LGPL 3
• orangeduck/LuaAutoC - Automagically use C Functions and Structs with the Lua API. License
• pfultz2/Cloak - A mini-preprocessor library to demostrate the recursive capabilites of the preprocessor. Boost
• skeeto/interactive-c-demo - Demonstration of interactive C programming. Unlicense
• symisc/PH7 - An Embedded Implementation of PHP (C Library). License
• yasm/yasm - Provides libyasm - embeddable YASM engine. License
• zserge/partcl - Micro Tcl implementation. MIT
• cesanta/mjs - Embedded JavaScript engine for C/C++. License
• graphitemaster/incbin - Include binary files in C/C++. Unlicense
• pkrumins/bithacks.h - bithacks.h is a C header file containing useful bit manipulation macros. MIT
• breckinloggins/ngtemplate - A template engine written in C designed to be syntax-compatible with Google CTemplate. MIT
• ccxvii/mujs - An embeddable Javascript interpreter in C. ISC
• Microsoft/checkedc - Extension to C that adds checking to detect or prevent common programming errors such as buffer overruns and out-of-bounds memory accesses. MIT
• hexspeakerg/ONLY_ONCE - ONLY_ONCE macro makes it so that the block of code is only run once across threads. MIT
• SanderMertens/flecs - An Entity Component System with a dashboard. MIT
• akeep/scheme-to-c - A small nanopass compiler from a subset of Scheme to C. MIT
• takanuva/ANSI-ISO-C-Exception-Handling - Exceptions in C. LGPL 3
• small-c/obj.h - A single-header support for OOP in pure C. MIT
• Hirrolot/poica - Features of modern programming languages in plain C11 implemented via macro system. MIT

^ Game Engines

• xonotic/darkplaces - Modified version of the Quake2 engine. GPL 2
• ioquake/ioq3 - The Quake3 engine, freed at last. GPL 2
• orx/orx - Portable, lightweight, plugin-based, data-driven, 2D-oriented game engine. License
• zturtleman/spearmint - Engine designed for FPS games. GPL 3
• Gigoteur/UnicornConsole - Unicorn Console: create quick game! MIT
• MarilynDafa/Bulllord-Engine - lightspeed lightweight elegant game engine in pure c. MIT
• HerculesWS/Hercules - Creation of a robust massively multiplayer online role playing game (MMORPG) server package. GPL 3
• Olde-Skuul/doom3do - The complete archive for DOOM for the 3DO. MIT
• RandyGaul/AsciiEngine - Game engine written in C to create Ascii art games within the Windows console. MIT
• littlewolf - The tiny software graphics and game engine. MIT
• eduard-permyakov/permafrost-engine - An OpenGL 3.3 RTS game engine written in C. GPL 3
• ejoy/ejoy2d - A 2D Graphics Engine for Mobile Game. MIT
• etlegacy/etlegacy - ET: Legacy is based on the source code of the Wolfenstein: Enemy Territory which was released under the GPLv3 license. GPL 3
• fabiensanglard/chocolate_duke3D - chocolate Duke Nukem 3D. License
• a-nikolaev/curseofwar - A Real Time Strategy game for Linux. GPL 3
• chocolate-doom/chocolate-doom - Chocolate Doom is a Doom source port that is minimalist and historically accurate. GPL 2
• cxong/cdogs-sdl - Classic overhead run-and-gun game. GPL 2
• fogleman/Craft - A simple Minecraft clone written in C using modern OpenGL (shaders). MIT
• id-Software/DOOM - DOOM Open Source Release. License
• id-Software/Quake-2 - Quake 2 GPL Source Release. GPL 2
• id-Software/Quake-III-Arena - Quake III Arena GPL Source Release. GPL 2
• id-Software/Quake - Quake GPL Source Release. GPL 2
• keendreams/keen - Keen Dreams on Greenlight! GPL 2
• linleyh/liberation-circuit - Trapped in a hostile computer system, you must make a way out - RTS/coding game. GPL 3
• martincohen/Punity - A tiny game engine in C. MIT
• orangeduck/Corange - Pure C Game Engine. License
• naev/naev - Naev is a 2d action/rpg space game that combines elements from the action, rpg and simulation genres. GPL 3
• nikki93/cgame - some ideas involving games and C. No license
• scottcgi/Mojoc - A cross-platform, open-source, pure C game engine for mobile game. MIT
• septag/darkhammer - darkHAMMER is a lightweight, open-source, multiplatform game engine. written in C (C99) language, supports python and C# bindings and lua scripts. License
• taylor001/crown - The flexible game engine. MIT
• theunamedguy/market-sim - A retro stock-trading game utilizing live market data. GPL 2
• tpoindex/crobots - CROBOTS is a programming game, for programmers (or aspiring programmers). GPL 2
• andwn/cave-story-md - A fan port of Cave Story for the Sega Mega Drive. License
• angband/angband - A free, single-player roguelike dungeon exploration game. License
• nesbox/tic.computer - Public TIC-80 issues tracker. MIT
• cschied/q2vkpt - Real-time path tracer VKPT integrated into q2pro Quake 2 client. GPL 2
• ec-/Quake3e - Improved Quake III Arena engine. GPL 2
• skullernet/q2pro - Enhanced Quake 2 client and server focused on multiplayer. GPL 2
• jdolan/quake2 - Classic Quake II for Mac and Linux. GPL 2
• nothings/obbg - Block/voxel-based game. Public domain
• bvschaik/julius - An open source re-implementation of Caesar III. AGPL 3
• simple2d/simple2d - Simple, open-source 2D graphics for everyone. MIT
• exezin/exengine - A C99 3D game engine. MIT
• NightDiveStudios/shockmac - System Shock (PowerMac version Official GPL Release). GPL 3
• blinry/gish - Open Source version of the award-winning physics platformer. Licenses
• ambethia/aposelene - Experimental 2D Engine in C. MIT
• klaussilveira/qengine - Retro game engine for developers that enjoy creating games like it's 1997. GPL 2
• sebbekarlsson/coelum - Game engine for 2d and 3d written in C. GPL 3
• bjornbytes/lovr - Virtual Reality Engine. MIT
• EvilPudding/candle - Game engine based on GLEW and SDL. MIT
• zauonlok/renderer - Shader-based software renderer in C89 with minimal dependencies. MIT
• cdev-tux/q3lite - Quake 3 engine rendered in OpenGL ES. GPL 3
• kondrak/vkQuake2 - Vulkan Quake 2 implementation. LGPL 2

^ Graphics Rendering

Everything related to video rendering only. Also visit awesome-opengl and awesome-vulkan.

• grimfang4/sdl-gpu - Library for high-performance, modern 2D graphics. Based on SDL. MIT
• dcnieho/FreeGLUT - Alternative to the OpenGL Utility Toolkit. Allows the creation and management of windows with OpenGL contexts. License
• MauriceGit/Cloth_Simulation - Cloth-Visualization via particle-simulation. ISC
• MauriceGit/Partikel_accelleration_on_GPU - Particle accelleration with OpenGL 4.3, using the compute shader to calculate particle movement on graphics hardware. ISC
• ands/lightmapper - A C/C++ single-file library for drop-in lightmap baking. Just use your existing OpenGL renderer to bounce light! Public domain
• ands/seamoptimizer - A C/C++ single-file library that minimizes the hard transition errors of disjoint edges in lightmaps. Public domain
• ebassi/graphene - A thin layer of graphic data types. MIT
• cacalabs/libcaca - ASCII renderer for terminal-based interfaces. WTFPL
• OpenGL - Industry adopted 2D and 3D graphics API. Graphics API
• OpenGL ES - Industry adopted 2D and 3D graphics API for mobile and embedded devices. Graphics API
• OpenGL SC - Graphic and compute standard for industry requiring system safety certification. Graphics API
• Vulkan - Explicit graphic and compute API for modern cross-platform development. Graphics API
• Cairo -2D graphics library. Licenses
• Cogl - GPU graphics and utilities API. License
• glfw/glfw - A multi-platform library for OpenGL, OpenGL ES, Vulkan, window and input. Zlib
• nigels-com/glew - The OpenGL Extension Wrangler Library. License
• anoek/ex-sdl-cairo-freetype-harfbuzz - Example code which uses SDL, cairo, freetype, and harfbuzz to do ttf/otf text layout and rendering. No license
• ashima/webgl-noise - Procedural Noise Shader Routines compatible with WebGL. MIT
• grz0zrg/fbg - Lightweight C 2D graphics API agnostic library with parallelism support. BSD 3-Clause
• ileben/ShivaVG - OpenGL based ANSI C implementation of the OpenVG standard. LGPL 2.1
• jpbruyere/vkvg - Vulkan vector drawing, try to stay close to cairo api. MIT
• memononen/nanovg - Antialiased 2D vector drawing library on top of OpenGL for UI and visualizations. Zlib
• micahpearlman/MonkVG - OpenVG 1.1 like vector graphics API implementation optimized for game use currently using an OpenGL ES backend that should be compatible with any HW that supports OpenGL ES 2.0 which includes most iOS and Android devices. License
• minusinf/opengl_dataviewer - A simple OpenGL xyzw dataviewer. GPL 3
• rougier/freetype-gl - OpenGL text using one vertex buffer, one texture and FreeType. License
• simple2d/simple2d - Simple, open-source 2D graphics for everyone. MIT
• jakogut/tinyflock - A simple, high-performance, threaded, and interactive flocking demo written in C with GLFW. No license
• anholt/libepoxy - Library for handling OpenGL function pointer management. License
• felselva/gfw - Pure C Minimal Graphics Framework (OpenGL). Zlib
• karimnaaji/voxelizer - Header only mesh voxelizer in c99. MIT
• kbernholm/leloup - All the C functions needed for drawing solid 3D vector graphics. MIT
• dr-soft/glbind - Single file OpenGL API loader. Licenses
• dr-soft/vkbind - Single file Vulkan API loader. Licenses
• dr-soft/minidraw - Single file 2D graphics library written in C. Licenses
• glouw/gel - N64-like software renderer. MIT

^ Gamedev Helping Libraries

• sigil - Sound, Input and Graphics Integration Library; a simple alternative to other libraries for doing all those things. Various licenses, all open source. Licenses
• SFML/CSFML - Binding for SFML in C. License
• SDL - Cross-platform development library designed to provide low-level access to audio, keyboard, mouse, joystick and graphics hardware via OpenGL. SDL2 is the most current version. Zlib
• HBehrens/obj2opengl - script to convert 3D models of OBJ files to C/C++ float arrays (vertices, faces, texture) compatible with OpenGL ES glDrawArrays compatible with iPhone/iPad. GPL 3
• Kazade/kazmath - A C math library targeted at games. BSD 2-Clause
• R4stl1n/cAudio - 3D Audio Engine Based on Openal. Zlib
• Tangent128/luasdl2 - A pure C binding of SDL 2.0 for Lua 5.1, Lua 5.2, and LuaJIT. ISC
• ccore/ccore_rewrite - A cross platform low level game development library. BSD 3-Clause
• cloudwu/skynet - A lightweight online game framework. MIT
• felselva/mathc - Pure C math library for 2D and 3D programming. Zlib
• gabomdq/SDL_GameControllerDB - A community sourced database of game controller mappings to be used with SDL2 Game Controller functionality. License
• geon/gloss - A bidirectional path tracer written in C. MIT
• jarikomppa/soloud - Free, easy, portable audio engine for games. License
• liballeg/allegro5 - The official Allegro 5 git repository. License
• recp/cglm - Highly Optimized Graphics Math (glm) for C. MIT
• raysan5/raylib - A simple and easy-to-use library to enjoy videogames programming. Zlib
• rxi/lovedos - A framework for making 2D DOS games in Lua. MIT
• slembcke/Chipmunk2D - A fast and lightweight 2D game physics library. MIT
• shaunlebron/blinky - Exploring peripheral vision in games (using Quake). MIT
• nem0/OpenFBX - Lightweight open source FBX importer. MIT
• librg/librg - Library for building simple and elegant cross-platform mmo client-server solutions. Apache 2
• Srekel/phyxed-2d - 2d physics engine with fixed-point support. Licenses
• recp/AssetKit - 3D asset importer/exporter/util library based on COLLADA/glTF specs. MIT
• olofson/audiality2 - A realtime scripted modular audio engine for video games and musical applications. Zlib
• dr-soft/miniobj - Simple library for loading OBJ mesh files. Public Domain
• dr-soft/mintaro - Framework for making simple, retro style games. Public Domain
• SasLuca/rayfork - raylib fork introducing some changes. No license
• jkuhlmann/cgltf - Single-file glTF 2.0 loader/writer in C99. MIT

^ Geography

Geodata, street maps, navigation and so on

• Unidata/gempak - Analysis, display, and product generation package for meteorological data. BSD 3-Clause
• evanmiller/ProjCL - Crazy-fast map projections and geodesic calculations. License
• olofsj/GLMap - An OpenGL ES 2.0 renderer for Openstreetmap data. LGPL 3
• olofsj/Whichway - C library for flexible (bike, foot, car) routing in road networks from Openstreetmap data. No license
• maxmind/geoip-api-c - GeoIP Legacy C API. License
• navit-gps/navit - The open source (GPL v2) turn-by-turn navigation software for many OS. License
• lionsoul2014/ip2region - Offline IP location library with accuracy rate of 99.9% and 0.0x millseconds searching performance. DB file is less then 5Mb with all ip address stored. binding for Java, PHP, C, Python, Nodejs, Golang, C#, lua. Binary, B-tree, Memory searching algorithm. Apache 2
• openvenues/libpostal - A C library for parsing/normalizing street addresses around the world. Powered by statistical NLP and open geo data. MIT
• propublica/simple-tiles - Simple tile generation for maps. MIT
• simplegeo/libgeohash - A pure C implementation of the Geohash algorithm. BSD 3-Clause
• kosma/minmea - Lightweight GPS NMEA 0183 parser library in pure C. WTFPL
• geocommons/geocoder - Modular Street Address Geocoder. LGPL 3
• bauerca/gridfloat - Slice and dice USGS elevation data from the command line. MIT

^ GUI

• tinyfiledialogs - Single-file library for simple dialogs. Compatible with many other toolkits and OSes. Zlib
• vurtun/nuklear - A single-header ANSI C gui library. Licenses
• andlabs/libui - Simple and portable (but not inflexible) GUI library in C that uses the native GUI technologies of each platform it supports. License
• lc-soft/LCUI - A small C library for building user interfaces with C, XML and CSS. MIT
• littlevgl/lvgl - Graphics library to create an embedded GUI with easy-to-use graphical elements, beautiful visual effects and low memory footprint. It offers anti-aliasing, opacity, and animations using only one frame buffer. MIT
• ocornut/imgui_club - Nice things to use along dear imgui. No license
• GTK+ - Cross-platform widget toolkit. License
• IUP - Another cross-platform widget toolkit. License
• Tk - Basic widget toolkit. Part of Tcl/Tk. License
• XForms Toolkit - Widget toolkit designed for the XWindow system. LGPL 2.1
• Clutter - UI library based on OpenGL. LGPL 2.1
• randrew/layout - Single-file library for calculating 2D UI layouts using stacking boxes. Compiles as C99 or C++. License
• cimgui/cimgui - c-api for imgui. MIT
• elvismt/slope - A library to create charts from raw data using cairo. Can be shown in GtkDrawingArea LGPL 3
• DeXP/nuklear_cross - Nuklear+ (read as "Nuklear cross") is a front-end overlay for Nuklear GUI library. Licenses
• xkbcommon/libxkbcommon - Keymap handling library for toolkits and window systems. License
• raysan5/raygui - Immediate GUI library from raylib author. Zlib
• rxi/microui - Immediate-mode UI ANSI C library. MIT
• VincentWei/minigui - Crossplatform windowing and GUI library targeted for embed usage. GPL 3
• achimdoebler/UGUI - Graphic library for embedded systems. License

^ Hardware Oriented

• obgm/libcoap - Implementation of the Constrained Application Protocol. License
• Genymobile/scrcpy - Display and control your Android device. Apache 2
• Azure/azure-iot-sdk-c - A C99 SDK for connecting devices to Microsoft Azure IoT services. MIT
• FoxelSA/libfastcal - Fast calibration data access. AGPL 3
• Stephane-D/SGDK - SGDK: A small, open and free development kit for the Sega Megadrive. MIT
• andygock/avr-uart - AVR UART C Library. License
• anrieff/libcpuid - a small C library for x86 CPU detection and feature extraction. BSD 2-Clause
• coocox/cox - CoX is an peripherals library with a unified standard interface specially for ARM Cortex M. BSD 3-Clause
• edorfaus/TEMPered - C library and program for reading the TEMPer family of thermometer and hygrometer devices. BSD 2-Clause
• google/cpu_features - A cross platform C99 library to get cpu features at runtime. Apache 2
• jackmitch/libsoc - C library for interfacing with common SoC peripherals through generic kernel interfaces. LGPL 2.1
• joan2937/pigpio - C library for the Raspberry which allows control of the General Purpose Input Outputs (GPIO). Unlicense
• libimobiledevice/libimobiledevice - A cross-platform protocol library to communicate with iOS devices. LGPL 2.1
• libopencm3/libopencm3 - Open Source ARM cortex m microcontroller library. GPL 3
• libusb/libusb - A cross-platform library to access USB devices. LGPL 2.1
• micronucleus/micronucleus - ATTiny usb bootloader with a strong emphasis on bootloader compactness. License
• nfc-tools/libnfc - Platform independent Near Field Communication library. LGPL 3
• signal11/hidapi - A Simple library for communicating with USB and Bluetooth HID devices on Linux, Mac, and Windows. Licenses
• wiiudev/libwiiu - Build system and examples for running C code on the Wii U. No license
• floooh/chips - 8-bit chip and system emulators in standalone C headers. Zlib
• rofl0r/endianness.h - Endianness detection and conversion. Licenses

^ Hashing

Hash function implementations for non-cryptographic purposes.

• centaurean/spookyhash - Fast hash function. BSD 3-Clause
• leo-yuriev/t1ha - Fast Positive Hash - a portable, fast hash function. BSD 3-Clause
• Cyan4973/xxHash - Extremely fast non-cryptographic hash algorithm. BSD 2-Clause
• PeterScott/murmur3 - Murmur3 hash in C. Public domain
• RJ/ketama - C library for consistent hashing, and langauge bindings. BSD 2-Clause
• cr-marcstevens/sha1collisiondetection - Library and command line tool to detect SHA-1 collision in a file. MIT
• clibs/hash - C hash implementation based on khash. MIT
• lemire/clhash - C library implementing fast CLHash function. Apache 2
• mattsta/crcspeed - This make CRC be fast. Included implementations: CRC-64-Jones and CRC-16-CCITT. BSD 3-Clause
• plashchynski/str2hex - Data formats convertion utility. Apache 2
• tzvetkoff/hashids.c - Port of the Hashids library. MIT

^ Image Processing and Computer Vision

• libgd/libgd - Library for the dynamic creation of images by programmers. License
• giflib - Library for reading and writing gif images. License
• libjpeg-turbo/libjpeg-turbo - Faster library for reading and writing JPEG files. Licenses
• libpng - The official PNG reference library. License
• liuliu/ccv - C-based/Cached/Core Computer Vision Library, A Modern Computer Vision Library. License
• Phildo/pixQL - SQL for image processing. No license
• XadillaX/byakuren - A theme color extracting library. MIT
• ansilove/ansilove - ANSi / ASCII art to PNG converter. BSD 2-Clause
• bluesmoon/pngtocss - Read in a gradient from a png file and spit out CSS for it. BSD
• brendangregg/Dump2PNG - Visualize file data as a PNG. License
• buaazp/zimg - A lightweight and high performance image storage and processing system. BSD 3-Clause
• dbohdan/s2png - Store data of any kind inside PNG images. GPL 2
• ginsweater/gif-h - Simple C++ one-header library for the creation of animated GIFs from image data. Unlicense
• libvips/libvips - A fast image processing library with low memory needs. LGPL 2.1
• mozilla/mozjpeg - Improved JPEG encoder. Licenses
• openslide/openslide - C library for reading virtual slide images. License
• pornel/giflossy - Lossy GIF compressor. GPL 2
• pornel/pngquant - Lossy PNG compressor. License
• rflynn/imgmin - Lossy image optimization. MIT
• uclouvain/openjpeg - Official repository of the OpenJPEG project. BSD 2-Clause
• vlfeat/vlfeat - An open library of computer vision algorithms. BSD 2-Clause
• libspng - Secure PNG reading/writing. BSD 2-Clause
• ImageMagick/ImageMagick - Image processing suite with C interface. License
• saitoha/libsixel - Library implementing the SIXEL protocol, allowing beautiful graphics in your terminal. License
• jedisct1/libpuzzle - A library to quickly find visually similar images. ISC
• mattes/epeg - Fast JPEG/ JPG thumbnail scaling with the minimum fuss and CPU overhead. It makes use of libjpeg features of being able to load an image by only decoding the DCT coefficients needed to reconstruct an image of the size desired. License
• dr-soft/dr_pcx - Single file PCX image loader. Public Domain
• cbraudo/qdbmp - Cross-platform C library for handling BMP files. MIT
• lecram/gifdec - GIF decoder. Public Domain
• gfxprim/gfxprim - Library for processing and drawing images in variety of formats. LGPL 2.1

^ Integrated Debugging and Logging

• gpakosz/whereami - One-file library for locating the current executable on the file system. MIT
• HardySimpson/zlog - Reliable, pure C logging library. LGPL 2.1
• esneider/debug - One-header library for easier 'printf debugging'. MIT
• ThrowTheSwitch/CException - Implementation of exceptions. License
• google/pblog - Small, low overhead, structured logging library intended for logging formware events. Apache 2
• 0xmalloc/c-log - a fast ,stable and thread-safe log lib(logger) for C/C++ language. Apache 2
• Celtoys/Remotery - Single C file, Realtime CPU/GPU Profiler with Remote Web Viewer. Apache 2
• armink/EasyLogger - A ultra-lightweight(ROM<1.6K, RAM<0.3k), high-performance C/C++ log library. MIT
• cyrus-and/prof - Self-contained C/C++ profiler library for Linux. License
• facebook/liblogfaf - A library that logs messages using non-blocking UDP datagrams. BSD 3-Clause
• kmcallister/embedded-breakpoints - Embed GDB breakpoints in C source code. BSD 3-Clause
• ntpeters/SimpleLogger - Basic logger for C and C++ projects. MIT
• openjudge/sandbox - Open-source suite of software components for C/C++ and Python developers to create automated profiling tools and watchdog programs. BSD 3-Clause
• rxi/log.c - A simple logging library implemented in C99. MIT
• yosefk/checkedthreads - checkedthreads: no race condition goes unnoticed! Simple API, automatic load balancing, Valgrind-based checking. BSD 2-Clause
• libFirm - Library that provides a graph-based intermediate representation, optimizations and assembly code generation suitable for use in compilers. Comes with an example C front-end under the same license. GPL 2
• daddinuz/watchdog - Memory tracer, leaks hunter. MIT
• okuvshynov/b63 - Lightweight benchmarking tool for C. Apache 2
• stephenrkell/trap-syscalls - Monitor, rewrite and/or otherwise trap system calls. Licenses
• immunityinc/libptrace - An event driven multi-core process debugging, tracing, and manipulation framework. LGPL 2.1

^ I/O

• Lajnold/falloc - falloc creates files of a user-specified size. It uses the posix_fallocate syscall for allocating the right size directly, instead of copying data like the commonly used dd tool does. GPL 3
• cgaebel/pipe - A simple thread-safe FIFO in C. MIT
• cxong/tinydir - Lightweight, portable and easy to integrate C directory and file reader. License
• reverbrain/eblob - Eblob is an append-only low-level IO library, which saves data in blob files. Created as low-level backend for elliptics. LGPL 3
• tronkko/dirent - C/C++ library for retrieving information on files and directories. MIT
• jwerle/fs.c - File system API much like Node's fs module. MIT
• zevv/duc - Library and suite of tools for inspecting disk usage. LGPL 3
• kwhat/libuiohook - A multi-platform C library to provide global keyboard and mouse hooks from userland.GPL 3
• dr-soft/dr_fs - Single file libraries for working with file system. Public Domain
• mpaland/printf - Standalone printf, sprintf and (v)snprintf implementation. MIT

^ Lexing and Parsing

• GNU Bison - General-purpose parser generator that converts an annotated context-free grammar into a range of parsers. GPL 3
• bbu/simple-interpreter - A hackable and extensible lexer, parser and interpreter for a minimalistic, imperative, C-like language. No license
• dcreager/libpush - An arrow-based parser combinator library for C. BSD 3-Clause
• kmussel/Moment - Natural Language Date Parser Using Lex/Yacc/C. MIT
• skvadrik/re2c - lexer generator for C/C++. License
• westes/flex - The Fast Lexical Analyzer - scanner generator for lexing in C and C++. License
• orangeduck/mpc - Parser combinator library. BSD 2-Clause
• transceptor-technology/libcleri - Libcleri is a powerful tool to build languages. From a built language, libcleri can automatically create parse trees, which are data structures representing how a grammar matches input. It also provides feedback in case the input does not match the language. This can be useful for auto-completion, suggestions or error handling. MIT
• dr-soft/url - URL parsing in C. BSD 2-Clause

^ Memory Management

• Boehm GC - Garbage collection for C. Various licenses, all open source. License
• Lockless Memory Allocator - Efficient memory allocator. GPL 3
• talloc - Hierarchical, reference-counted memory pool system with destructors. LGPL 3
• mattconte/tlsf - Two-Level Segregated Fit allocator; a general-purpose, dynamic memory allocator designed to meet real-time requirements. BSD 3-Clause
• jemalloc/jemalloc - General purpose malloc(3) implementation that emphasizes fragmentation avoidance and scalable concurrency support, commonly used in production systems. License
• dlmalloc - Doug Lea's malloc(3) implementation, useful for academic and research purposes. Public domain
• CCareaga/heap_allocator - A simple heap memory allocator in ~200 lines. MIT
• ivmai/bdwgc - The Boehm-Demers-Weiser conservative C/C++ Garbage Collector (libgc, bdwgc, boehm-gc). License
• mulle-nat/mulle-allocator - Flexible C memory allocation scheme with leak checking. BSD 3-Clause
• munificent/mark-sweep - A simple mark-sweep garbage collector in C. MIT
• ned14/nedmalloc - Fast portable thread caching malloc implementation written in C for multiple threads without lock contention based on dlmalloc. Optimised for x86 and x64. Compatible with C++. Can patch itself into existing binaries on Windows. Boost
• orangeduck/tgc - A Tiny Garbage Collector for C. BSD 2-Clause
• rampantpixels/rpmalloc - Public domain cross platform lock free thread caching 32-byte aligned memory allocator implemented in C. License
• stevedekorte/garbagecollector - Incrementall garbage collector library in C for use by high level language implementions. BSD 3-Clause
• Simon-Swenson-8351/tralloc - A binary tree based memory allocator. BSD 3-Clause
• Qqwy/raii_with - A simple library to provide RAII in standard-compliant C99. MIT
• emeryberger/Malloc-Implementations - A collection of memory allocators. No license
• microsoft/mimalloc - Compact general purpose allocator by Microsoft. MIT
• mjansson/rpmalloc - Cross platform lock free thread caching 16-byte aligned memory allocator. License
• yvan-sraka/malloc - malloc implementation with reduced dependencies. GPL 3
• AlxHnr/CRegion - Region-based memory management library. License

^ Multimedia

Audio and video processing.

• jeremyevans/ape_tag_libs - Library for working with APEv2 tags. MIT
• lieff/minimp3 - Lightweight MP3 decoder single header library. License
• FFMPEG - Complete, cross-platform solution to record, convert and stream audio and video. LGPL 2.1
• GStreamer - Framework for audio and visual media. LGPL 2
• mpv-player/mpv - Media player MPV with provided library libmpv. Compile with ./waf configure --disable-cplayer --enable-libmpv-shared to not have the music player. License
• andrewrk/libsoundio - Library for cross-platform, real-time audio input and output. Has a range of back-ends. MIT
• AVbin/AVbin - Thin, cross-platform wrapper around Libav’s video- and audio-decoding functionality, providing long-term binary compatibility for applications and languages that need it. LGPL 3
• PaulBatchelor/Soundpipe - A lightweight music DSP library. MIT
• Themaister/libfmsynth - A C library which implements an FM synthesizer. MIT
• UniversalPrimer/flv-analyzer - Loads an FLV file into sane C data structures and outputs fields as human readable. GPL 3
• Vidvox/hap-qt-codec - A QuickTime codec for Hap video. License
• acrisci/playerctl - mpris command-line controller and library for spotify, vlc, audacious, bmp, cmus, and others. LGPL 3
• aubio/aubio - a library for audio and music analysis. GPL 3
• cmatsuoka/libxmp - Libxmp is a library that renders module files to PCM data. License
• cnlohr/colorchord - Chromatic Sound to Light Conversion System. BSD 3-Clause
• csound/csound - A sound and music computing system. LGPL 2.1
• dxjia/ffmpeg-commands-executor-library - execute ffmpeg commands through a jni shared library. Apache 2
• erikd/libsndfile - A C library for reading and writing sound files containing sampled audio data. LGPL 2.1
• kfish/libfishsound - A simple programming interface for decoding and encoding audio data using Xiph.org codecs (FLAC, Speex and Vorbis). BSD 3-Clause
• libass/libass - libass is a portable subtitle renderer for the ASS/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. ISC
• libav/libav - Collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata. License
• mltframework/mlt - MLT Multimedia Framework. LGPL 2.1
• sahib/glyr - Glyr is a music related metadata searchengine, both with commandline interface and C API. LGPL 3
• simonyiszk/csdr - A simple DSP library and command-line tool for Software Defined Radio. License
• xiph/flac - Free Lossless Audio Codec. License
• xiph/opus - Modern audio compression for the internet. License
• mhroth/tinyosc - A minimal Open Sound Control (OSC) library written in vanilla C. ISC
• libao - Cross-platform audio library with a wide variety of outputs. GPL 2
• libvlc - VLC player library. Licenses
• raysan5/raudio - A simple and easy-to-use audio library based on miniaudio. Zlib
• dr-soft/miniaudio - Single file audio playback and capture library written in C. Licenses

^ Multiple Purpose Libraries

• parallella/pal - Optimized library for maths, parallel processing and data movement. Apache 2
• APR - Apache Portable Runtime; another library of cross-platform utility functions. Apache 2
• GLib - Library of utility functions and structures, designed to be portable, efficient and powerful. LGPL 2.1
• keybuk/libnih - Lightweight library of C functions and structures. GPL 2
• wolkykim/qlibc - Simple and powerful C library, designed as a replacement for GLib while focusing on being small and light. License
• chutsu/cog - C common library containing common data structures, sorting algorithms and utility functions. MIT
• cs50/libcs50 - CS50 Library for C. MIT
• dcreager/libcork - A simple, easily embeddable cross-platform C library. BSD 3-Clause
• faragon/libsrt - C library for writing fast and safe C code, faster. It provides string, vector, bit set, set, map, hash set, and hash map handling. Suitable for soft and hard real-time. Allows both heap and stack allocation. BSD 3-Clause
• koanlogic/libu - LibU is a multiplatform utility library written in C, with APIs for handling memory allocation, networking and URI parsing, string manipulation, debugging, and logging in a very compact way, plus many other miscellaneous tasks. License
• letoram/arcan - Display Server, Multimedia Framework, Game Engine-> "Desktop Engine". Licenses
• saprykin/plibsys - Highly portable C system library: threads and synchronization primitives, sockets (TCP, UDP, SCTP), IPv4 and IPv6, IPC, hash functions (MD5, SHA-1, SHA-2, SHA-3, GOST), binary trees (RB, AVL) and more. Native code performance. MIT
• tboox/tbox - A glib-like multi-platform c library. Apache 2
• zpl-c/zpl - Your C99 Powerkit. Licenses
• dmw/caffeine - C Application Framework. LGPL 2.1
• breckinloggins/libuseful - A collection of useful data structures, algorithms, and utilities for C programming. MIT
• erimatnor/libckit - A kit of C-based utilities and data structures. Apache 2
• pforemski/libpjf - A C library of data structures with tools (based on libasn). GPL 3
• stevedekorte/basekit - C based OO portable data structure library. BSD 3-Clause
• mjansson/foundation_lib - Cross-platform foundation library in C providing basic support data types and functions to write applications and games in a platform-independent fashion. Unlicense
• happyfish100/libfastcommon - Functions including: string, logger, chain, hash, socket, ini file reader, base64 encode / decode, url encode / decode, fast timer, skiplist, object pool etc. detail info please see the c header files. LGPL
• sabit/libcprops - C prototyping tools. LGPL 2.1

^ DNS

• GNU adns - Advanced, easy-to-use, asynch-capable DNS client library and utilities. GPL 3
• ldns - Library to simplify DNS programming. BSD 3-Clause
• bagder/c-ares - Library for asynchronous DNS requests. License
• farsightsec/dnstable - encoding format, library, and utilities for passive DNS data. Apache 2
• wahern/dns - Single file non-blocking DNS C library without callbacks or external dependencies. MIT
• libidn - Implementation of the Stringprep, Punycode and IDNA specifications. Licenses
• mjansson/mdns - mDNS/DNS-SD library. Unlicense

^ HTTP

• nodejs/http-parser - HTTP request/response parser for c. MIT
• h2o/picohttpparser - Tiny HTTP parser. MIT
• iafonov/multipart-parser-c - Http multipart parser implemented in C. MIT
• solusipse/ureq - Micro C library for handling HTTP requests on low resource systems. MIT
• nghttp2/nghttp2 - HTTP/2 C Library. MIT
• wg/wrk - Modern HTTP benchmarking tool. License

^ Mail

• libquickmail - Library intended to give developers a way to send email from their applications. Supports multiple To/Cc/Bcc recipients and attachments without size limits. GPL 3
• dinhviethoa/libetpan - Mail Framework for C Language. License
• dertuxmalwieder/libvldmail - Your friendly e-mail address validation library. WTFPL

^ Messaging and Brokers

• nanomsg/nng - Lightweight brokerless messaging. MIT
• alanxz/rabbitmq-c - Client library for RabbitMQ. License
• antirez/disque - Disque is a distributed message broker. BSD 3-Clause
• circonus-labs/fq - [email protected]#$*&%Q (Message queue that is fast, brokered, in C and gets out of your way). MIT
• zeromq/czmq - High-level C binding for ØMQ. License
• nanomsg/nanomsg - C-based implementation of ZeroMQ. License
• LiamBindle/MQTT-C - MQTT protocol implementation. MIT

^ Remote Desktops

• FreeRDP/FreeRDP - FreeRDP is a free remote desktop protocol library and clients. Apache 2
• LibVNC/libvncserver - LibVNCServer/LibVNCClient are cross-platform C libraries that allow you to easily implement VNC server or client functionality in your program. GPL 2

^ RPC

• hmng/jsonrpc-c - JSON-RPC in C. MIT
• lopter/lightsd - A daemon with a JSON-RPC API to control your light bulbs. GPL 3
• laruence/yar - RPC for C and PHP. License
• protobuf-c/protobuf-c-rpc - Using protobuf-c for RPC. License

^ TCP, UDP, Sockets

• bovine/datapipe - Network TCP port forwarding. Public domain
• sch3m4/libntoh - User-friendly C Library to perform TCP streams reassembly and IPv4/6 defragmentation. License
• tass-belgium/picotcp - PicoTCP is a free TCP/IP stack implementation. Licenses
• opendp/dpdk-odp - Open data plane on dpdk, TCP/IP stack for dpdk. BSD
• lsalzman/enet - ENet reliable UDP networking library. MIT
• hoxnox/rawsock_recv_example - SOCK_RAW IPPROTO_UDP socket data transmission example. BSD 3-Clause
• silentbicycle/socket99 - C99 wrapper for the BSD sockets API. ISC
• fastos/fastsocket - Fastsocket is a highly scalable socket and its underlying networking implementation of Linux kernel. GPL 2
• sustrik/msg_control - Helper functions for dealing with socket ancillary data. MIT

^ Web Servers

• taf2/libebb - Lightweight high-performance HTTP server library for C. MIT
• libhttpd - Library to add basic web server capabilities to an application or embedded device. LGPL
• libmicrohttpd - Small C library that makes it easy to run an HTTP server as part of another application. Licenses
• risoflora/libsagui - Cross-platform C library which helps to develop web servers or frameworks. LGPL 3
• h2o/h2o - Optimized HTTP/1, HTTP/2 high performance server/library. MIT
• mongrel2/mongrel2 - The Mongrel2 Web Server Project. BSD 3-Clause
• shenfeng/tiny-web-server - a tiny web server in C, for daily use. MIT
• zyearn/zaver - Yet another fast and efficient HTTP server. MIT
• libsoup - GNOME HTTP client/server library. Uses GObject. LGPL 2
• criticalstack/libevhtp - Create extremely-fast and secure embedded HTTP servers with ease. BSD 3-Clause
• civetweb/civetweb - Embedded C/C++ web server. Licenses
• lpereira/lwan - Experimental, scalable, high-performance HTTP server. GPL 2
• cesanta/mongoose - Embedded web server for C/C++. License
• oneoo/alilua - epoll/kqueue+lua based web server. MIT
• haywire/haywire - Haywire is an asynchronous HTTP server framework written in C that's built using the event loop based libuv platform layer that node.js is built on top of. Apache 2
• davidmoreno/onion - C library to create simple HTTP servers and Web Applications. Licenses
• wolkykim/libasyncd - Embeddable Event-based Asynchronous Message/HTTP Server library for C/C++. BSD 2-Clause
• balde/balde - Microframework for C based on GLib. LGPL 2.1
• bitly/simplehttp - A family of libraries and daemons for building scalable web infrastructure. MIT
• boazsegev/facil.io - Your high performance web application C framework. MIT
• iafonov/cosmonaut - Fast web server & micro framework implemented in C. Just for fun. MIT
• riolet/WAFer - WAFer is a C language-based software platform for scalable server-side and networking applications. Think node.js for C programmers. GPL 2
• jeremycw/httpserver.h - Single header library for writing non-blocking HTTP servers in C. MIT
• lammertb/libhttp - Crossplatform HTTP and HTTPS library. MIT
• zhaojh329/libuhttpd - Fully asynchronous HTTP server library based on libev and http-parser for embedded Linux. MIT
• silgy/silgy - Multipurpose asynchronous web application backend engine. MIT

^ Web Service APIs

• sinemetu1/twitc - Mini library for interacting with the Twitter OAuth API. MIT
• dajobe/flickcurl - Flickr C API library. GPL 2
• Cotix/cReddit - CLI Reddit client written in C. Includes separated library. License
• HalosGhost/shaman - A small, native C library and utility to fetch weather. GPL 2
• PromyLOPh/pianobar - Console-based pandora.com player. License
• Yubico/yubico-c-client - Yubico C client library. BSD 2-Clause
• adobkin/libcapn - A simple C Library for interact with the Apple Push Notification Service (APNs). MIT
• aws/aws-iot-device-sdk-embedded-C - SDK for connecting to AWS IoT from a device using embedded C. Apache 2
• domsson/libtwirc - Twitch IRC library for Linux. License

^ Websockets

• tatsuhiro-t/wslay - WebSocket library. Implements version 13 of the WebSocket protocol, as described in RFC 6455. MIT
• JonnyWhatshisface/libwebsock - Easy-to-use and powerful web socket library. LGPL 3
• m8rge/cwebsocket - Lightweight websocket server library. MIT
• zhaojh329/libuwsc - A Lightweight and fully asynchronous WebSocket client C library based on libubox for Embedded Linux. LGPL 2.1
• warmcat/libwebsockets - Canonical websocket library. `License
• wbudd/RingSocket - Lockless multi-threaded C11 Linux WebSocket server. MIT
• clemenskresser/ezwebsocket - Websocket server library in C. MIT

^ Uncategorized Networking

• libcurl - Client-side URL transfer library, supporting a wide range of formats. License
• oSip - SIP implementation in C without additional dependencies. LGPL
• rxi/dyad - Asynchronous networking library. MIT
• 51Degrees/Device-Detection - Device detection for C / PHP / Perl / Python and Node.js - professionally maintained device data. License
• uriparser/uriparser - Strictly RFC 3986-compliant URI parsing and handling library. BSD 3-Clause
• c9s/r3 - High-performance path dispatching library. It compiles your route paths into a prefix tree (trie). By using the constructed prefix trie in the start-up time, you may dispatch your routes with efficiency. MIT
• versatica/OverSIP- OverSIP: the SIP framework you dreamed about. MIT
• libssh2/libssh2 - the SSH library. BSD 3-Clause
• rockdaboot/mget - Multithreaded metalink/file/website downloader (like Wget) and C library. LGPL 3
• seanmiddleditch/libtelnet - Simple RFC-complient TELNET implementation as a C library. Public domain
• shadeslayer/libnice - Implementation of the IETF's Interactive Connectivity Establishment (ICE) standard (RFC 5245) and the Session Traversal Utilities for NAT (STUN) standard (RFC 5389). Licenses
• udp/lacewing - Cross-platform network I/O library for C/C++. License
• verse/verse - Network protocol for real-time sharing between graphical applications. Licenses
• the-tcpdump-group/libpcap - the LIBpcap interface to various kernel packet capture mechanism. BSD 3-Clause
• the-tcpdump-group/tcpdump - the TCPdump network dissector. BSD 3-Clause
• luohaha/CSpider - A scalable and convenient crawler framework. MIT
• nitrogenlogic/cliserver - A sample libevent-based network socket server that presents a simple command line interface to multiple connecting clients. BSD 2-Clause
• babelouest/ulfius - Web Framework to build REST APIs, Webservices or any HTTP endpoint in C language. Can stream large amount of data, integrate JSON data with Jansson, and create websocket services. LGPL 2.1
• haiwen/ccnet - Ccnet is a framework for writing networked applications in C. GPL 2
• it4e/CHL - C Hypertext Library - A library for writing web applications in C. LGPL 3
• jorisvink/kore - An easy to use, scalable and secure web application framework for writing web APIs in C. License
• monkey/duda - Duda I/O is an event-driven and high performant web services framework which exposes a friendly C API. Apache 2
• zeromq/zyre - Framework for proximity-based peer-to-peer applications. License
• Maxime2/dataparksearch - Open source, feature rich search engine. License
• kristapsdz/kcgi - Minimal CGI and FastCGI library for C/C++. ISC

^ OpenCL

OpenCL, CUDA, OpenMP and other similar APIs.

• cf4ocl - The C Framework for OpenCL. LGPL 3
• clMathLibraries/clRNG - an OpenCL based software library containing random number generation functions. License
• tuxfan/ocl-mla - OpenCL Mid-Level Abstractions. License
• matze/oclkit - Two-file OpenCL wrapper. GPL 3
• emrainey/OpenCL-Environment - A series of utilities aimed at making OpenCL easier to use. Apache 2

^ OS Specifics

• symisc/libcox - Library which permits cross-platform system calls and standard utilities across different operating systems. BSD 2-Clause
• checkpoint-restore/criu - Checkpoint/Restore In Userspace; a software tool (with a C API) for 'freezing' a running application to disk, then restoring it. Targeted for Linux. Licenses
• alsa-lib - Userspace library to interact with ALSA. LGPL 2.1
• Leandros/WindowsHModular - A modular Windows.h Header. License
• a0rtega/pafish - Pafish is a demonstration tool that employs several techniques to detect sandboxes and analysis environments in the same way as malware families do. GPL 3
• antirez/linenoise - A small self-contained alternative to readline and libedit. BSD 2-Clause
• fancycode/MemoryModule - Library to load a DLL from memory. License
• jimon/osx_app_in_plain_c - A simple showcase how to create a simple OS X app in plain C without any Objective-C. No license
• rvoicilas/inotify-tools - Library and a set of command-line programs for Linux providing a simple interface to inotify. GPL 2
• tinyalsa/tinyalsa - Tiny library to interface with ALSA in the Linux kernel. BSD 3-Clause
• wengkai/ACLLib - A bunch of C functions covers Win32API and provides simpler API to beginners for programming Windows GUI applications. GPL 3
• zardus/preeny - Some helpful preload libraries for pwning stuff. BSD 2-Clause

^ Procedural Generation

• prideout/heman - Tiny library of image utilities dealing with height maps, normal maps, distance fields and the like. MIT
• JCash/voronoi - A C implementation for creating 2D voronoi diagrams. MIT
• Srekel/the-worldinator - Procedural world generation experiment. Licenses
• saxbophone/libsxbp - Experimental generation of 2D spiralling lines based on input binary data. License
• ajxs/pbp - Procedural Block Painter. Experiments in procedural art generation. MIT
• Tastyep/ProceduralNoise - Useful functions for procedural generation. No license

^ Processes and IPC

• D-Bus - Interprocess communications bus. Licenses
• bus1/dbus-broker - Linux D-Bus Message Broker. Apache 2
• signalapp/libsignal-protocol-c - Signal Protocol C Library. GPL 3
• sharvil/flingfd - A tiny library to send file descriptors across processes. Apache 2
• sheredom/process.h - A simple one header solution to launching processes and interacting with them for C and C++. Unlicense
• troydhanson/kvspool - A library to support streaming data applications. MIT
• xroche/coffeecatch - Tiny native POSIX signal catcher (especially useful for JNI code on Android/Dalvik). BSD 2-Clause
• samuellab/InterProcess - A compact C library to share data between processes on Windows. GPL 3

^ Regex and Search

• kkos/oniguruma - Regex library supporting a wide range of encodings, and incorporating many security-oriented fixes. BSD 2-Clause
• PCRE - Implementation of regexes identical to that of Perl 5. License
• nasciiboy/RecursiveRegexpRaptor-4 - Simple and complete implementation of regular expressions with its own sintax. GPL 3
• laurikari/tre - POSIX-compliant, feature-full regex library. License
• cesanta/slre - Super Light Regexp engine for C/C++. License
• k-takata/Onigmo - Regular expressions library forked from Oniguruma. License
• openresty/sregex - A non-backtracking NFA/DFA-based Perl-compatible regex engine matching on large data streams. BSD 3-Clause

^ Serialization

• dvidelabs/flatcc - FlatBuffers compiler and library. Apache 2
• liteserver/binn - Binary serialization format meant to be compact, fast and easy-to-use. Apache 2
• jmckaskill/c-capnproto - Implementation of the Cap'n Proto serialization protocol. MIT
• apache/avro - Avro data serialization system for several languages, including C. Apache 2
• liteserver/netstring-c - Netstring encoder and decoder. Public domain
• protobuf-c - Implementation of Google Protocol Buffer in C. License
• ErikDubbelboer/c-pack - Simple data packing/unpacking in C. No license
• acg/lwpb - Lightweight Protocol Buffers for C and Python. Apache 2
• camgunz/cmp - An implementation of the MessagePack serialization format in C. MIT
• cloudwu/pbc - A protocol buffers library for C. MIT
• cloudwu/sproto - Yet another protocol library like google protocol buffers ,but simple and fast. MIT
• dryman/opic - Fast serialization framework for C. LGPL 3
• google/upb - Small protobuf implementation in C. BSD 3-Clause
• greghaynes/Afproto - Serial data framing protocol. License
• ludocode/mpack - Encoder/decoder for the MessagePack serialization format. MIT
• nanopb/nanopb - Protocol Buffers with small code size. Zlib
• troydhanson/tpl - Small binary serialization library for C. License
• clibs/dumpasn1 - Display the contents of ASN.1 encoded data. License
• vlm/asn1c - The ASN.1 Compiler. BSD 2-Clause
• eerimoq/pbtools - Google protobuf tools. MIT

^ Source Code Collections

• DanielGibson/Snippets - Useful code snippets and header-only libraries. Public domain
• CCAN - Modelled after Perl's CPAN, this is a big collection of C code. No license
• libdjb - Collection of libraries doing various things. License
• BurntSushi/clibs - A smattering of miscellaneous C libraries. Includes sane argument parsing, a thread-safe multi-producer/multi-consumer queue, and implementation of common data structures (hashmaps, vectors and linked lists). WTFPL
• RandyGaul/cute_headers - Collection of cross-platform one-file C/C++ libraries with no dependencies, primarily used for games. Licenses
• chadjoan/C-Survival-Kit - A set of useful functions, data structures, and macros aimed at allowing more expressive and reliable C code. Portability targets are OpenVMS and Linux. Boost
• floooh/sokol - Minimal cross-platform standalone C headers. Zlib
• gingerBill/gb - Single-file public domain libraries for C & C++. Public domain
• gozfree/libraries - Basic libraries all written in c by gozfree, including network, event, config, log, hash, ipc, rpc, mem, and so on. MIT
• mackron/dr_libs - A collection of public domain single-file libraries for C/C++. Public domain
• mattiasgustavsson/libs - Single-file public domain libraries for C/C++. Public domain
• matteobertozzi/carthage - Pure C Data Structure and Utils. BSD
• napsy/libhelper - General functions and data structures for C. BSD 3-Clause
• niklasfrykholm/nflibs - A collection of interoperable minimalistic C libraries. `Public domain
• nothings/stb - Single-file public domain libraries for C/C++. Licenses
• prideout/par - Single-file C libraries from Philip Allan Rideout. MIT
• rmitton/rjm - Various single-file C libraries. Public domain
• vurtun/mmx - single header libraries for C/C++. No license
• yl790/algorithms-and-data-structures - Different algorithms & data structures. No license
• rofl0r/libulz - a collection of useful functions and data structures to create C apps faster. focus on simplicity, ability to statically link and minimal binary size. LGPL 2.1
• sdroege/snippets - Some algorithms and data structures. LGPL 3
• lbrito1/cstuff - Algorithms & data structures in C. GPL 2
• angelortega/mpdm - Minimum Profit Data Manager. Public domain
• attractivechaos/klib - Small and lightweight implementations of common algorithms and data structures. MIT
• f1nalspace/final_game_tech - Game related libraries. MIT
• QwertyQaz414/anv - Collection of header-only utility libraries. MIT

^ Scientific

Math mostly located in Calculations category

• GuillaumeHolley/BloomFilterTrie - A data structure for pan-genome storage. MIT
• noporpoise/seq_file - Library for Reading Bioinformatic Sequence Data in C. Public domain
• r0nk/corvus - Genetic BF programming. No license
• XenonofArcticus/DynamicTrack - Access sources of dynamically-updated data about discrete entities like GPSes, INSes, ADS-B sources. MIT
• ericmandel/funtools - A "minimal buy-in" FITS library and utility package for astronomical data analysis. LGPL 2.1

^ Special Purpose

Libraries with very narrow non-generic purpose.

• TulipCharts/tulipindicators - Library of functions for technical analysis of financial data. LGPL 3
• MatthewLM/cbitcoin - Low-level bitcoin library written in C. MIT
• RhysU/ESIO - Provides simple, high throughput input and output of structured data sets using parallel HDF5. ESIO is designed to support reading and writing turbulence simulation restart files within C, C++, and modern Fortran applications. LGPL 2.1
• Unidata/netcdf-c - Official GitHub repository for netCDF-C libraries and utilities. BSD 3-Clause
• jgarzik/picocoin - A bitcoin library in C, SPV wallet & more. License
• libtrading/libtrading - Ultra low-latency trading connectivity library for C and C++. BSD 2-Clause
• nayuki/QR-Code-generator - High-quality QR Code generator library in Java, JavaScript, Python, C++, C. MIT
• qiq/Czech-morphology - Czech morphology library, using data files compatible with PDT 2.0 License
• sleuthkit/sleuthkit - The Sleuth Kit® (TSK) is a library and collection of command line digital forensics tools that allow you to investigate volume and file system data. The library can be incorporated into larger digital forensics tools and the command line tools can be directly used to find evidence. Licenses
• hroptatyr/uterus - universal tick encoder library to efficiently transport huge amounts of tick data. BSD 3-Clause
• luke-jr/bfgminer - Modular ASIC/FPGA miner written in C, featuring overclocking, monitoring, fan speed control and remote interface capabilities. GPL 3

^ Standard Libraries

Implementations of the C standards

• PDCLib - The Public Domain C Library. Implements most of C99 and some of C11. License
• uClibc-ng - Small C library for developing embedded systems. LGPL 2.1
• dietlibc - C standard library designed for the smallest possible binaries. GPL 2
• glibc - The GNU C Library; an implementation of the C standard library. Licenses
• musl - Standard C library, compatible with POSIX 2008 and C11. Designed for static linking. MIT
• NuxiNL/cloudlibc - CloudABI's standard C library. BSD 2-Clause
• marssaxman/startc - Minimal freestanding C library for bare-metal i386 development. License
• olibc/olibc - Another C Library optimized for Embedded Linux. BSD
• lpsantil/rt0 - A minimal C runtime for Linux i386 & x86_64. BSD 2-Clause
• keith-packard/picolibc - Standard C library APIs that targets small embedded systems with limited RAM. Licenses

^ String Manipulation

• wooorm/levenstein.c - Levenstein distance algorithm implementation. MIT
• wooorm/stmr.c - Porter Stemmer algorithm implementation. MIT
• websnarf/bstrlib- The Better String Library. BSD 3-Clause
• ICU - International Components for Unicode; a library for Unicode support. License
• libunistring - Library for manipulating Unicode strings in C. Licenses
• libgiconv - Text conversion library. LGPL
• JuliaStrings/utf8proc - Small, clean library for processing UTF-8 Unicode data. License
• antirez/sds - Simple Dynamic Strings library for C. BSD 2-Clause
• boyerjohn/rapidstring - Maybe the fastest string library ever. MIT
• clibs/buffer - Tiny C string library. MIT
• chrisjmccormick/word2vec_commented - Commented (but unaltered) version of original word2vec C implementation. Apache 2
• fontforge/libuninameslist - A library with a large (sparse) array mapping each unicode code point to the annotation data for it. BSD 3-Clause
• jasonmaclafferty/String - Dynamic string data type implementation. MIT
• josephg/librope - UTF-8 rope library for C. MIT
• sheredom/utf8.h - Single header utf8 string functions for C and C++. Unlicense
• branchless-utf8 - Branchless UTF-8 decoder. Unlicense
• g-berthiaume/strsepf - Single header string parsing function with memory safety of strsep and the convenience of a sscanf-like interface. MIT
• karlmcguire/sing - String ring buffer library. MIT

^ Testing

• yhfudev/cpp-ci-unit-test - A modern minimal hassle unit test framework. MIT
• codeplea/minctest - Unit testing microlibrary. Zlib
• evolutional/utest - Single-header unit testing library. Unlicense
• Tuplanolla/cheat - Very simple unit testing framework. BSD 2-Clause
• libcheck/check - Unit testing framework for C. LGPL 2.1
• ThrowTheSwitch/CMock - Mock/stub generator for C. MIT
• cmocka - Unit testing framework with support for mock objects. Apache 2
• rafael-santiago/cutest - Library for unit testing with memory leak detection (Linux, FreeBSD and Windows). GPL 2
• nemequ/munit - Small but full-featured unit testing framework for C with no dependencies. MIT
• zorgnax/libtap - Write tests in C. LGPL 3
• Snaipe/Criterion - A cross-platform C and C++ unit testing framework for the 21th century. MIT
• ThrowTheSwitch/Unity - Simple Unit Testing for C. MIT
• bvdberg/ctest - Unit test framework for software written in C. Apache 2
• clear-code/cutter - An easy to write and debug unit testing framework for C and C++. Licenses
• compiler-dept/speck - A small unit testing framework for C. MIT
• joewalnes/tinytest - A tiny unit-testing framework for C. No license
• lpabon/cmockery2 - Reviving cmockery unit test framework from Google. Apache 2
• mcandre/qc - C port of the QuickCheck unit test framework. BSD 2-Clause
• mchochlov/Gnucash - Data model unit testing - GSoC 2011. Licenses
• mortie/snow - A testing library for C. MIT
• orangeduck/ptest - DRY Microtesting Framework for C. BSD 3-Clause
• silentbicycle/greatest - A C testing library in 1 file. No dependencies, no dynamic allocation. ISC
• silentbicycle/theft - property-based testing for C: generate input to find obscure bugs, then reduce to minimal failing input. ISC
• siu/minunit - Minimal unit testing framework for C. MIT
• stephenmathieson/describe.h - Simple BDD describe test. MIT
• vmg/clar - What tests are made of. ISC
• CuTest - C Unit Testing Framework. Licenses
• eerimoq/nala - Test framework for C projects. Based on narwhal and narmock. MIT
• vberlier/narwhal - Framework for writing readable and maintainable tests for C programs and libraries. MIT
• vberlier/narmock - Finds the functions mocked in your tests and generates mocks. MIT
• sheredom/utest.h - Single header unit testing framework. [Unlicense][80-61]
• Koldar/crashc - Automatic C source code testing framework. MIT
• christophercrouzet/rexo - Unit testing framework for C and C++. Unlicense

^ TUI

Textual User Interface

• sabotage-linux/netbsd-curses - Simplified and small version of curses, with the same interface. Licenses
• ncurses - Coloured terminal UI library. Licenses
• doches/progressbar - An easy-to-use C library for displaying text progress bars. BSD 3-Clause
• jwerle/progress.c - Progress display lib for c. MIT
• nsf/termbox - Library for writing text-based user interfaces. MIT
• alandekok/recli - A re-imagined CLI. Customizable syntax, help, permissions, data types. BSD 2-Clause
• matthiasbock/ucurses - Very small and simple text-based user interface (TUI) library for microcontrollers. GPL 3
• serameo/TUI - Text User Interface using curses for UNIX. GPL 3
• jakubfi/emui - Text user interface toolkit. License
• nejohnson/stui - Simple Text User Interface. BSD 3-Clause
• tboox/ltui - A cross-platform terminal ui library based on Lua. Apache 2
• okbob/ncurses-st-menu - ncurses based library for CUA look menu. BSD 2-Clause
• LionyxML/nocurses - A terminal screen manipulation library. GPL 2
• seleznevae/libfort - Crossplatform library for formatted text tables creation. MIT
• LiquidityC/termesc - ANSI escape TUI library. No license
• tryggth/newt - TUI library made by RedHat. License
• serameo/TUI2 - TUI fox Unix. No license

^ Uncategorized

• recp/tm - Timer and Timeline Utils for C. MIT
• libgit2/libgit2 - Pure C implementation of Git. License
• ThomasHabets/monotonic_clock - Portable C library for getting monotonic time. BSD 3-Clause
• graphviz - Graph Visualization Tools. License
• h2non/semver.c - semantic version parser and serializer written in ANSI C. MIT
• libical/libical - Libical is an Open Source implementation of the iCalendar protocols and protocol data units. Licenses
• jonpe960/ufsm - UML Statechart library in C and XMI importer. BSD 3-Clause
• locasto/libdisorder - A simple C library for entropy measurement of byte streams and other data. GPL 2
• lucasb-eyer/heatmap - High performance C heatmap generation library. Supposed to be wrapped by higher-level languages. MIT
• tailhook/objpath - A library that allows to traverse data structures by path. MIT
• pornin/CTTK - Constant-Time Toolkit. MIT
• juliettef/IconFontCppHeaders - C, C++ headers and C# classes for icon fonts: Font Awesome, Fork Awesome, Material Design, Material Design icons, Kenney game icons and Ionicons. Zlib
• eam/libcrange - Range parsing library for managing sets of ostnames, ips, clusters, roles and other operational data. BSD 3-Clause