These are some great First Person Shooter games that are free and open source. If you would like to download and play any of these you can find the links provided down below.
Find more free open source games at http://www.tjfree.com/free-open-source-games/
Download Links:
Xonotic: https://www.xonotic.org/download/
Red Eclipse: https://www.redeclipse.net/
Saurbraten: http://sauerbraten.org/
Terminal Overload: http://www.terminal-overload.org/
FreeDoom: https://freedoom.github.io/
