Cheeky Fingers - Piano Chord Dictionary, Progressions and Suggestions
Flowkey - The easiest way to learn piano with your iPhone or iPad
Synthesia - A fun way to learn how to play the piano.
Yousician - Learn to play music at home, at your own pace
Musicope - The Piano Game. Contribute to oldrich-s/musicope development by creating an account on GitHub.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.