The Source engine is a 3D game engine developed by Valve Corporation. Its unique features include a large degree of modularity and flexibility, an artist-driven, shader-based renderer, accurate lip sync and facial expression technology, and a powerful, efficient and completely network-enabled physics system.
VTFEdit is a VTF texture conversion utility with a graphical interface. It can convert to and from and view all versions of the Valve Texture Format, and change the files' settings without requiring them to be recompiled.
VTFEdit is developed by Nem. Visit his website for more details.