what is idtech?
id Tech. id Tech is  a series of separate 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 2, 3, and 4 have been released as free software under the GNU General Public License, along with the source code to Wolfenstein 3D, Doom, and Quake.