Tremulous

Tremulous is a game which blends a team based FPS with elements of a real-time strategy. Players can choose from 2 unique races, aliens and humans. Both teams are able to build working structures in-game like an RTS. These structures provide many functions, the most important being spawning. Other structures provide base defence, healing functions and much more. As a human, players are rewarded with credits for each alien kill. These credits may be used to purchase new weapons and upgrades. Aliens are able to evolve into a new class.

download: http://prdownloads.sourceforge.net/tremulous/tremulous-1.1.0-installer.exe?download