Flowkey - The easiest way to learn piano with your iPhone or iPad
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.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Synthesia - A fun way to learn how to play the piano.
HDpiano - HDpiano is the Netflix of Piano Tutorials.