Alternatives to osu!

Guitar Hero clone

Kart racing game

Extensible rhythm game engine based on StepMania

Frontend for emulators, game engines and media players (OpenGL graphics API)

Real-time strategy game

Open-source transport simulation game

Multiplayer online battle arena game

Game launcher with the ability to run Windows games

Audio player

Indoor cycling game

Client for Old School RuneScape

Open-source, cross-platform game engine designed to be used by everyone