Simply Piano - Fast and fun way to learn piano
Synthesia - A fun way to learn how to play the piano.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Linthesia - Linthesia is a game. A game of playing music! You only need a MIDI file
Yousician - Learn to play music at home, at your own pace
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.