Build

The Build engine was a first-person shooter engine created by Ken Silverman for 3D Realms. Like DOOM, the Build engine created its world using different 2D shapes (called sectors) on a 2D grid. Each sector could have a specified ceiling and floor height. When the game ran the engine rendered these sectors as 3D even though geometrically it was stored as 2D.

Labeled as a 2.5D engine, the Build engine allowed for more complex worlds than DOOM. It was called 2.5D as it came with tools called sector tags that could let the level designer make a world that appeared to be fully 3D. For example, one sector tag would make a player fall through the floor if he walked over it and teleport him to another sector. In essence this would be used to create the effect of falling down a hole to a bigger room or creating a surface of water that could be jumped into to explore underwater. While these made the game appear to be 3D it wouldn't be until later FPS games, like Quake, that the engine actually stored the game as 3D information.

The Build engine was most famous for powering the classic 3D Realms FPS Duke Nukem 3D. The engine was used in at least 12 published games (Witchaven, William Shatners' TekWar, Shadow Warrior, Blood, PowerSlave and Redneck Rampage being the next most well known).