Top 4 vtf open source projects

uSource is a plugin for importing MDL / BSP / VMT / VTF and etc... resources to Unity!

VTFLib is a LGPL open source programming library that provides a C and C++ API for reading and writing Valve VTF and VMT format image files.

C# parsers and formats for Half-Life 1 and related engines.

Three.js loader for parsing Valve's Source Engine models