Singularity!

Unvanquished is a free, open-source first-person shooter combining real-time strategy elements with a futuristic, sci-fi setting. It is available for Windows, Linux, and Mac OS X.

The Hammer of Thyrion project is a cross-platform source port effort of Raven Software's Hexen.

Nexuiz was originally developed by Lee Vermeulen and Forest ‘LordHavoc’ Hale, who started Alientrap in the summer of 2002. The goal of the project was to create a high quality first person shooter that could be played freely across all platforms in one package: PC, Mac, and Linux. The engine that powered Nexuiz was Forest Hale’s Darkplaces engine.

Bulletstorm focuses on combat, both with firearms and melee attacks. There are a variety of fictional firearms available, although the game also places heavy emphasis on kicking enemies and using the energy leash.

The game begins in 1923, after World War I veteran Patrick Galloway receives an urgent letter from his friend Jeremiah Covenant. Covenant, well aware of Galloway's reputation for dealing with occult matters, is in failing health and raves about a curse that has destroyed his entire family. Galloway travels to the Covenant estate on the coast of Ireland to visit his friend, who relates an outlandish tale of supernatural terrors.

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... »

SUPERHOT is the first person shooter where time moves only when you move. No regenerating health bars. No conveniently placed ammo drops. It's just you, outnumbered and outgunned, grabbing the weapons of fallen enemies to shoot, slice, and maneuver through a hurricane of slow-motion bullets.

Master time to become the ultimate weapon! Dr. Aiden Krone has made a Time Jump across the space-time continuum - a reckless act with frightening consequences. Now, a disturbing alternate reality has evolved within the bleak and rain-soaked Alpha District.