I asked this a while ago which is how I discovered Beyond All Reason which has been my FOSS game of choice as of late.
I’d also recommend Naev and Endless Sky (Both are based on the Escape Velocity Series, Naev is getting a 3D PBR renderer in the next release). Mindustry is good fun, actually purchased this one on steam to support the amazing developer. Extreme Tux Racer is a bit of fun and Super Tux Kart seems to get better with every update (did I mention it can run on the Nintendo Switch via homebrew!)
Edit: I forgot about 0ad and Minetest which I used to play a bit of a while back
Xonotic (quake-esque FPS, IMO its like quake and halo had a FOSS child), Minetest (a voxel game engine, multiple games are available for it), and Mindustry (sandbox tower defense) are the only ones ive tried so far
I still haven’t tried it, but I’ve heard how great Veloren apparently is. It’s an MMO voxel game that takes inspiration from Zelda: Breath of the Wild and is written in Rust.
Super Tux Kart (I play it on Android) is NOT one of them. The physics system is bad at some moments, the items aren’t fun to use and some of them ruin the game. The overall game feels amateurish (in a bad way), but one thing that I like is the Windows Car and the drifting. Those are awesome.