Team Fortress 2 (lost original builds of PC game; 1999-2006)
This article has been tagged as Needing work due to its lack of information (classes in Brotherhood of Arms, 2006 build differences, etc).
Team Fortress 2 is a free-to-play first-person shooter game developed by Valve, who also developed the previous Team Fortress Classic and other acclaimed shooters such as Half-Life. It's one of the most popular games on Steam and has generally been well received for its gameplay and community aspects. The game has gone through many different builds and prototypes since its inception and was originally going to be much different to the final product. The art style alone, according to Valve themselves, went through three to four different phases before they finally settled on the current design.
Brotherhood of Arms (1999)
The first build of the game, originally announced at E3 1999, was going to share a similar art style to the original Team Fortress, and was to be dubbed "Brotherhood of Arms".
This version would've been significantly different from previous Team Fortress games. The gameplay, maps, and weapons were going to take a more realistic approach, and there were going to introduce 12 classes, rather than the 9 classes from the final game.
The second build of the game was leaked in 2003. Unlike the previous build, this version was less realistic and would have probably taken place in the Half-Life universe. Two models of the build were found in Half-Life 2's code and could be accessed via cheats. This build would have had NPCs present during multiplayer matches and more futuristic weapons. The classes would have been the same as its modern counterparts, except for the Demoman class, which would have been replaced with a "sapper" class. Instead of red and blue teams, there would have been an alien team and a human team. Concept art and a few models have surfaced which can be found on the Team Fortress 2 wiki as well as a fan-made a build of the game using found models and textures.
Final Design (2006)
Team Fortress 2 was re-announced in 2006. In the July of the same year, Electronic Arts and Valve Software revealed the final design of the game. The conference and Valve screened two teaser trailers demonstrating the game. The trailers showed a build of the game that was similar to the original but had some differences in it. These included weapons from the original Team Fortress Classic game, nearly finished designs of the characters with things that weren't in the final design of the game (examples like the Spy and 2Fort) and gameplay as well.
A few things from the build are in the current version of the game, but things such as models and maps were not in the game. However, some modders have attempted to create these elements for the released game. The only remaining evidence of this build are the trailers from the conference itself and pre-release screenshots that appear on most gaming sites.