I bought a $1 Steam game called Square Brawl some 5 years ago. It's a minimalistic arena battle with forgiving physics, diverse and satisfying weapons and a geometric design based on squares.

It's among my favourite couch multiplayer games, but the programming is shit. The resolution is weird, the launcher is some default config screen that came with the game engine, with a controller it's tricky to avoid picking a second color by accident which spawns a ghost player that is jointly controlled by the AI and the player. Sometimes the game spawns 10 copies of everyone, all of which you control at the same time. Getting stuck inside walls is commonplace.

On an unrelated note, I'm making a minimalistic arena battle with forgiving physics, diverse and satisfying weapons and a geometric design based on squares. It's gonna be FOSS and web-based. I haven't settled on a name yet but I think Tetragon Tussle might be good.