Multi-player coop game. There's a demo too. The game was updated with hi-res textures and the frame-rate-limit removed in 2015 ( https://www.rockpapershotgun.com/tag/castle-crashers/
"Hack, slash, and smash your way to victory in this newly updated edition of the insanely popular 2D arcade adventure from The Behemoth! Up to four friends can play locally or online and save your princess, defend your kingdom, and crash some castles!"