Id Tech

id Tech is the family of game engines designed and developed by id Software. Prior to the presentation of the id Tech 5-based game Rage, the engines lacked official designation and as such were simply referred to as the Doom and Quake engines, from the name of the main game series the engines have been developed for. id Tech numbers 1, 2, 3, and 4 have been released as free software under the GNU General Public License.

According to Eurogamer.net, "id Software has been synonymous with PC game engines since the concept of a detached game engine was first popularised." However id Tech 4 had far fewer licensees than the Unreal Engine from Epic Games, and id plans to regain the momentum with id Tech 5.