While most haven't yet heard of the Unvanquished game, it's a promising but yet-to-be-officially-released open-source multi-player game.
Earlier today I was tipped off by a Phoronix reader about Unvanquished, following my recent controversial comments about most open-source game artwork being awful. "I read your article on how Open Source programs (for the most part) are awful. I agree with this to some extent, but I would like to show you some of the animation models in Unvanquished. It is an Open Source game which is still in Alpha, but the models are absolutely amazing in comparison to the game it is branching off from (Tremulous)."
When visiting Unvanquished.net the web-site just says "coming soon", but if following the links there is a Wiki and SourceForge download links. The files up on SourceForge are from June. The development of this multi-platform game is also being done in the open and can be found on GitHub where the most recent commit is just four hours ago!
The Unvanquished Wiki explains the game as:
Unvanquished is a free open-source first-person shooter and strategy game with 3D graphics 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).
While the humans are equipped with weapons that they use to exterminate the alien presence, the aliens have only their pincers and a few special attacks, such as poison gas, and ranged electrical and projectile attacks. Players do not spawn at random points in the map; instead, each map has default spawn points and both teams are capable of moving them wherever they please. Both teams have other buildings that round out their base, such as machinegun turrets for the humans and barricades for the aliens. Either team wins by destroying the opposing team's spawn points and killing any remaining members of that team before they are able to build any more spawn points or the game timer ends.
This Daemon engine for Unvanquished features a voice-say system, navigation-mesh-based bot AI, a legacy OpenGL renderer along with an OpenGL 3.x renderer from XreaL, Stereoscopic 3D renderer support, MD3 and MD5 model support, an improved shader system, procedural animation blending, VoIP support, in-game IRC, and localization support.
While this game is still in alpha and hasn't been formally introduced to the open-source gaming community at large, so far it appears to be very promising. But then again, the original XreaL was extremely promising in its early days. However, I wish Unvanquished the absolute best of luck seeing as there's a real need for more Linux-native open-source games of high quality.
For those that care just about the end result rather than the technical details, embedded below are some YouTube videos about Unvanquished.
Not bad at all for a community-based open-source title! It's still not to the quality of Unreal Engine 4 (or UE3), Valve's Source Engine, or Unigine, but it's extremely nice for coming out of the open-source community.