Stick Fight, Duck Game, TowerFall Ascension, and Overcooked come to mind.
Stick Fight and Duck Game are both platform combat games where each player gets one life per level, pick up guns and melee weapons and beat the crap out of one-another.
TowerFall is also a platform combat game but you use a bow almost exclusively as your primary weapon and get modifiers for it. It also has a co-op mode that is a bit of fun.
Overcooked is a cooperative task management game where players work together making different dishes by preparing and combining ingredients. It's a lot of fun, very hectic, and definitely caused more than one divorce (probably).