As it does so very kindly like to do, id Software has released another dollop of engine source code. This latest is somewhat less exciting than many, simply offering the updated Doom 3 source from the BFG Edition but hey, now the folks at home can make the best and shiniest Doom 3 games yet.
As with id's other recent source releases, it's up on GitHub for your coding conveniences. Or you can download the full pack from Shacknews. Of course, just because the engine source has been released, it doesn't mean BFG Edition is free--all the game data and assets are still protected.
Id has also dropped a new patch for the BFG Edition on PC, bringing fixes and a whole heap of new menu options to play with.