Synthesia - A fun way to learn how to play the piano.
Metronaut - An app to help you play classical music
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
Violin by Trala - Violin by Trala is a music learning app that is designed specifically for Violin users.
Playground Sessions - Online piano learning game.
Simply Piano - Fast and fun way to learn piano