Force: Leashed is a free first person gravity fiddler. To advance, you need to guide rockets to their targets using spherical potential fields. And no, it's not like Portal. That much.
Force: Leashed was started as one of the 2012 7DFPS prototypes. It is based on GPL-licensed Darkplaces which for example also powers Xonotic.
Force: Leashed is available for free download for Linux, Mac OS X and Windows from its website.
The art asset license status is unknown. Watch this tweet for further information.
Of about 150 entries at the first seven day first person shooter development jam (7DFPS), so far I could identify two prototypes that have clear open source licensing in their code and run.
Note that this contest did not require sources to be released, only 19 entries had theirs released at time of writing.
Cannonball Z is a game where you shoot zombies with cannonballs. It features randomly generated maps.The source code is in the .zip file. The engine uses a BSD license. My code is GPL and my assets are CC BY-SA.
OxyFPS is a simple first person shooter with the restriction of being in an oxygen-lacking environment.You are on an airless planet with only a suit, a crossbow and a tank of air.Your objective is to survive as long as you can while the corporate goons that caused this terraforming catastrophe hunt you down.