Unvanquished

Unvanquished is a first-person shooter and strategy game created by Unvanquished Development. Players fight online in team based combat in a war of aliens against humans. The game is available for most major platforms (Linux, Mac and Windows). Support for other platforms (e.g., BSD) is partially completed but not officially supported.

While the humans are equipped with conventional weapons—ranging from the standard-issue rifle to the powerful Lucifer Cannon—the aliens fight with pincers, mandibles, electrical, and projectile attacks. The game has a high emphasis on team-play: lone players are easy pickings for an opposing team who travels in groups. RTS-like strategy comes into play in the form of base-building: each map has a default base for both teams, but players are free to expand or move however they please. Similarly, a team wins by destroying the opposing team's spawn points and killing any remaining members of that team before they are able to rebuild.

Minimum system requirements: 

CPU: 1.8 GHz
RAM: 1024 MB
GPU: OpenGL 2.0-compatible