Id Tech 3

id Tech 3, originally known as the Quake III Arena engine, is a game engine developed by id Software for its 1999 game Quake III Arena. It has subsequently been used in numerous games. Commercially, id Tech 3 competed with early versions of the Unreal Engine; both were widely licensed. Originally proprietary, it is now open-source software.

id Tech 3 is based on the earlier id Tech 2, with a large amount of the code rewritten. id Tech 4 was derived from id Tech 3, as was Infinity Ward's IW engine, used in Call of Duty 2 onward.