[airforce1]

I think the video game "Dead Cells" was created by a co-op

[EddieDante]

Yes, a French co-op.

[turtledove]

See also The Glory Society, KO_OP, Lucid Tales, Triple Topping, Future Club, Soft Not Weak, Stray Bombay, Pixel Pushers Union 512, Hopoo, Chromatic Games, to name a few other coop games studios.