Duke Nukem Forever is a 2011 first-person shooter video game for Windows, OS X, PlayStation 3, and Xbox 360. It is a sequel to the 1996 game Duke Nukem 3D as part of the long-running Duke Nukem series. Duke Nukem Forever entered development in 1997 at 3D Realms and Triptych Games and was finished by Gearbox Software and Piranha Games in 2011. In the game, the player controls Duke Nukem, an action hero who must come out of retirement and save the world from aliens when they begin kidnapping the women of Earth.
Due to the game's long development cycle, several prototypes are lost to time.
At the 1998 Electronic Entertainment Expo, a prototype was show off, claiming to be based off of id software's Quake 2 engine (which was later used for the critically acclaimed Quake III Arena). People were surprised at this, because nobody thought that id and 3D Realms would get together to make a Duke game.
Later, in 2001's E3, another prototype was shown off, this time in Epic Games' Unreal Engine, mainly used for tournament arena shooter games like Unreal Tournament. This prototype showed full AI compatibility thanks to Epic Games. This build was 90% complete before being scrapped, and is out there, somewhere.
Development went quiet in 2002, before the game's eventual release in 2011.