CONV. - Convert YouTube video to MP3, GIF or MP4
Synthesia - A fun way to learn how to play the piano.
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
Playground Sessions - Online piano learning game.
Yout - YouTube to Mp3 Converter
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.