Gang Brawlers is a classic side-scrolling beat-'em-up: you walk right, enemies arrive, and you punch and kick them until they don't. Crates break open into weapons and items, and two players can fight through it together on one keyboard.
The genre lives or dies on whether the combat feels good, and this one gets the basics right — attacks have weight, and picking up a pipe genuinely changes a fight.
Yes — two players share one keyboard with their own control sets, which is how the beat-'em-up genre is meant to be played.
Back toward a wall or the edge of the screen so enemies can only approach from one side, and clear that side before moving on.
Yes — a 2D game with nothing to install.