Synthesia - A fun way to learn how to play the piano.
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Playground Sessions - Online piano learning game.
music21 - Music21 is a Python-based toolkit for computer-aided musicology.
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
Harmony Assistant - Harmony Assistant is an unbeatable software for computer-assisted music composition and editing.