id Software has said for several years that it intends to release the Doom 3 source code after Rage shipped, and now those plans are looking a little more concrete. During his legendary QCon keynote speech yesterday, id technical wizard John Carmack revealed that parent company ZeniMax has approved the source release, and it'll arrive some time after Rage's October launch (via Eurogamer).
Carmack explained that ZeniMax approved of id's plans to release the source, though it'll still need to be run by legal. The source code also needs a bit of a polish first, he said. Carmack also called on other games developers to release their source code, as it helps budding devs learn the ropes.
What does the source code release mean for your average player? Plenty! Thanks to the open source code, past id games have been updated by the community with bug fixes, improved compatibility with modern hardware, and new features ranging from updated menus and netcode to astounding graphics improvements. It'll enable mods to become standalone releases, playable by people who don't have Doom 3. Then there'll undoubtedly be brand new games, both free and commercial, built upon the engine.
What it won't mean is free Doom 3. While the engine source code will be open, this won't include the game's assets (levels, artwork, sounds, and all that jazz) so you'll still need to buy it to play.
While id's past source releases have waited until all games which licensed the engine were out the door, there's still one id Tech 4 game in development: Prey 2. However, Human Head is almost certainly using a newer version of the engine than that seen in Doom 3, and has "heavily modified" it anyway.