Since we had a half day on Friday, November 17, we held a virtual gaming meeting!
SuperTuxKart
One of the most iconic FLOSS games on Linux is SuperTuxKart! This game combines all of your favorite FOSS mascots (Konqi KDE, The GNU, and of course, Tux!), along with a vast selection of other characters via the vibrant assortment of Add-Ons available!
STK has a variety of maps, characters, and even a drifting skidding
mechanic not unlike that one proprietary "Nine ten do" game!
Xonotic
Xonotic is a Quake-engine based, GPLv3 multiplayer shooter with fast-paced action through amazing movement mechanics. Quite a fun time when you can find someone else to play with. This is a bit on the more gory side, but there is a setting to turn that off if you'd rather keep it a bit more family-friendly ;)
Modes include deathmatch, where players compete for the most kills, along with team modes, races, and "Capture the Flag" modes with less hacking and much more frantically running around trying not to get instagibbed :P
Pokémon Showdown
Seth tells me that Pokémon Showdown is technically FOSS! This is a (mainly JS-based) simulator for battles in your favorite pocket monster catching games, with a web client and vibrant online community.
Modes are available for many generations of the Pokémon games, along with imaginary "fakemons", and standard tournament-level game rules.