Meludia - Listening exercises and to sharpen your ear and music theory skills
Synthesia - A fun way to learn how to play the piano.
GNU Solfege - GNU Solfege is free music education software.
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
Perfect Ear - A simple yet advanced application for improving your solfege skills.
Playground Sessions - Online piano learning game.