Source 2007 (by valve)
4.0
Application background
Valve's Source Engine 2007 was used in barely any titles, but was used by modders to create custom games.
I recommend you secure a license with Valve before using this in any of your titles.
You need to have the DirectX 2010 SDK in order to compile this build of Source Engine.
Key Technology
Valve's Source Engine uses it's own proprietary file system format (AKA the *.vpk format) that was used in titles later than 2007.
OpenGL and DirectX 9 support
Xbox and PS3 support
Linux/Mac support
Valve has their own custom sound engine that's based off of DirectX's DirectAudio (Although depreciated, can work wonders)