Commonly known as the "Doom 3 engine" which was used to power Doom 3 as it released in 2004, id Tech 4 began as an enhancement to id Tech 3.
Other games using this engine were Raven Software's Quake 4 (2005) and Wolfenstein (2009), Human Head Studios' Prey (2006), Splash Damage's Enemy Territory: Quake Wars (2007) and Brink (2011).