1. SerpentineC++/Win32/Boost Windows RAT (Remote Administration Tool) with a multiplatform Java/Spring RESTful C2 server and Go, C++/Qt5 frontends
2. Connmapconnmap is an X11 desktop widget that shows location of your current network peers on a world map (tested only with i3wm). Made with C and libcairo.
3. rconnrconn is a multiplatform program for creating generic reverse connections. Lets you consume services that are behind firewall or NAT without opening ports or port-forwarding.
4. revpReverse HTTP proxy that works on Linux, Windows, and macOS. Made with C++ and Boost.