Duke Nukem Forever (lost original builds of first-person shooter sequel; 1997-2009)
Duke Nukem Forever is notable for having one of the longest development cycles in gaming history, starting development in 1997, and releasing in 2011. The game had gone through numerous changes prior to release, including two builds that are now considered lost.
The game started off development using the Quake II engine, in 1998. A trailer was subsequently released.
However, 3D Realms made the decision to switch to the Unreal Engine, a process that was to take a month to 6 weeks. In 1999, they released screenshots that showcased what could be achieved with the Unreal Engine, and shortly after, stated that the game would see a 2000 release.
In 2001, another trailer was released, which shown various improvements over Duke Nukem 3D, with the trailer ending with the phrase "When it's ready". In 2002, the game was reworked yet again with another engine, with most of the original designs being reworked or scrapped. They announced that the game would be released in 2004, when it was announced that it had been reworked again, with the Doom 3 engine.
In 2008, several screenshots were bundled as unlockable extras in the XBLA release of Duke Nukem 3D. Then, in 2009, the development took an unexpected turn. 3D Realms was downsized, which resulted in the large majority of the development team being laid off.
More gameplay was also leaked online. This is assumedly of one of the last builds.
The game was then remade, from scratch, by 2K Games and Gearbox.