Tremulous is a free open source game that blends team based FPS with RTS. Players can choose from 2 unique races: aliens and humans. Players on both teams are able to build bases from a handful of different structures. These structures provide a multitude of functions, such as allowing players to respawn after dying. The builders must ensure there are spawn structures or other players will not be able to rejoin the game after death. Other structures can be built to provide some amount of automated base defence, or heal wounded players and much more.