Flowkey - The easiest way to learn piano with your iPhone or iPad
Metronaut - An app to help you play classical music
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Violin by Trala - Violin by Trala is a music learning app that is designed specifically for Violin users.
Simply Piano - Fast and fun way to learn piano
Real Piano Teacher - Real Piano Teacher is a music learning application that lets you learn how to play the piano, organ, flute, Guitar, and many other instruments just in seven days.