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.
Utilize Valve’s existing tools for monitoring video, network, and game entity performance.
What Is This? I do not Know this program.
It is the in-game developer tools. A great example is with portal 2, there is a tool that draws the paths that players and objects take when flung by a faith plate