StepMania - Rhythm game for Windows, Mac, and Linux.
Osu - Osu is Music, Rhythm, Single and Multiplayer video game developed by Dean Herbert.
Clone Hero - Clone Hero is a free rhythm game, which can be played with any 5 or 6 button guitar controller...
McOsu - A free open-source circle-clicking rhythm game practice client for osu!
Frets on Fire - Bonus content.
Deemo - Deemo comes with a Music-based Rhythm video game that features only Single-player mode and is available to play on Multiple Platforms.