id Software may not have quite the degree of independence that it once did, at least since being acquired by ZeniMax, but the developer hasn't abandoned its tradition of friendliness to the open-source community. A tweet by id tech guru John Carmack suggests that the source code for Doom 3 is on the verge of going public:
@adamix_ doom 3 source is packaged and tested, we are waiting on final lawyer clearance for release.
id Software usually waits for engine licensees to release their games commercially before it makes the engine source code available to the public. I believe the last commercial game to use the Doom 3 engine was Brink, which shipped in May. id also released the source code for Quake III in 2005, Quake II in 2001, Quake in 1999, and Doom in 1997. Those open-source releases have bred a variety of modified game engines, some enhancing the original id titles with new graphical effects, and others powering entirely new games.
I wonder if we'll see Rage's id Tech 5 engine go open source in a few years. Unlike past id engines, this one won't be licensed outside the ZeniMax family. Developers who want to use the engine will have to have their games published by Bethesda.