Doom3 Source Code Review: Introduction (Part 1 of 6) >> On November 23, 2011 id Software maintained the tradition and released the source code of their previous engine. This time is was the turn of idTech4 which powered Prey, Quake 4 and of course Doom 3. Within hours the GitHub repository was forked more than 400 times and people started to look at the game internal mechanisms/port the engine on