Teeworlds

Teeworlds (formerly TeeWars) is a free, open-source sidescrolling multiplayer shooting game originally created by the Swedish developer Magnus Auvinen and now maintained by the community. It features simple cartoon-themed graphics and physics and relies heavily on classic shooter weaponry and gameplay. Currently there are official versions for Microsoft Windows, Linux, macOS as well as being available via the digital distributor Steam since 2015.