Flowkey - The easiest way to learn piano with your iPhone or iPad
Synthesia - A fun way to learn how to play the piano.
Jameasy for Violin - Play rhythm game with a real violin. you can play with background music and real-time feedback
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
alphaTab - alphaTab is a cross platform music notation and guitar tablature rendering library.
Playground Sessions - Online piano learning game.