Tremulous

Tremulous is a free, open source game that blends a team based FPS with elements

of an RTS. Players can choose from 2 unique races, aliens and humans. Players on

both teams are able to build working structures in-game like an RTS. These

structures provide many functions, the most important being spawning. The

designated builders must ensure there are spawn structures or other players will

not be able to rejoin the game after death. Other structures provide automated

base defense (to some degree), healing functions and much more...

Tremulous client.