id Software has just launched their official account on GitHub.
All of the Id open source releases are now on github: github.com/id-Software
— John Carmack (@ID_AA_Carmack) January 31, 2012
The company said that this section would offer all their open source projects.
They already are offering a bunch of them including:
Doom 3 GPL source release
Wolfenstein 3D for iOS Source Release
DOOM Classic for iOS Source Release
Quake GPL Source Release
DOOM Open Source Release