SuperTuxKart is probably at least a candidate if it has to be FOSS

Minetest Server(Minigame or Survival)

There are some DOOM death match wads? Or Probably Unreal Tournament.

Battle Craze, yes please! It's a fighting game, relatively all ages I think.

• It's free.
• Not resource intensive, i.e. only about 500mb!
• It's multiplayer.
• It's really, really fun.
• It's a passion project developed by a really small team.
• It needs more players.

Altitude would be fun to see reborn. Hit 4-5k players at its peak on Steam. Now pretty much dead apart from dedicated league play.

It's a 2D flight/arena game with a variety of game modes, aircraft to fly, weapons, perks, powerups etc. Very arcade.

• ✅ Fun
• ✅ Accessible (Win/Mac/Linux/Steam)
• ✅ All ages
• ✅ Casual (games last minutes, not hours)
• ✅ Not AAA
• ✅ Free
• ✅ Runs on potato

Only drawback according to the assignment:

• ❌ Not FOSS

Beyond All Reason is incredibly fun and approachable. It's a completely open source strategy game that's basically built for big battles, 8v8 is the most popular mode.

I think fighting games would make a good community, maybe with friendly tournaments organized regularly. The free ones that i know of are the hololive one (idol showdown) from steam and the emulated arcade titles from fightcade.

Veloren

If you opened this up to free-only Steam games, that would probably get you a ton more players. Almost everything works on Linux now unless theres some kind of aggressive anticheat.

You can see a list of free multiplayer games here

Werewolf

I put together a large list of categorized Linux compatible games, many of which are multiplayer, all if them are free, and each entry lists their open-source status. Hopefully y'all can find some good ones there for this group :)

Personally, I suggest OpenSpades

Im always up for some older classics

Been playing some Battlefield 1942... legally... and Battlefield 2 has multiple options for playing actually legally.

I miss the era where it was fun, rather than min/max games