Is there a FOSS tag on Steam? Can we make one? I think if we are enough to tag FOSS game as FOSS, Steam may catch on.
You can just add one to games. Hit the + button on the page and type FOSS.
It's probable that Steam doesn't want to do that. Otherwise I imagine it would be there already.
You could use a Curator profile for that though.
I recognize that the list hasn't been updated in a long time (almost all of the Android games have not had commits for 7+ years), but one I would recommend is LibreSudoku. It's just normal Sudoku, but by nature of it being FOSS it beats the alternatives.
Hey, get MapTools up on there. It's my go-to Remote TableTop (RTT) for pencil and paper gaming over the internet. Sure, learning curve's a teensy bit thicker, and I have to run the server, but I can run weird game systems and write macros without getting nickel and dimed.
While working on a multiplayer games library, we are also making higher quality open-source web game demos, for those interested: https://docs.joinplayroom.com/templates