The DOOM 3 source as it was released under the GPL license on November 22, 2011.

The original release of the DOOM 3 source code on GitHub was done by Timothee
'TTimo' Besset on November 22, 2011.  To properly maintain the metadata between
the various forks on GitHub since then and the creation of the id-Software GitHub
account on January 31, 2011, I've forked TTimo's repository and then forced a
hard reset to the first commit.

This leaves the current "official" release from id Software just as it was on
November 22, 2011, but allows interested developers to track down interesting
work being done in TTimo's branch and all over GitHub.

Cheers,

Travis Bradshaw