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