Flowkey - The easiest way to learn piano with your iPhone or iPad
Clone Hero - Clone Hero is a free rhythm game, which can be played with any 5 or 6 button guitar controller...
Yousician - Learn to play music at home, at your own pace
StepMania - Rhythm game for Windows, Mac, and Linux.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Osu - Osu is Music, Rhythm, Single and Multiplayer video game developed by Dean Herbert.