UltraStar Deluxe - A free and open source karaoke game inspired by the Singstar™ game, runs on Windows, Linux and macOS.
Synthesia - A fun way to learn how to play the piano.
Yokee - Karaoke to YouTube videos
Playground Sessions - Online piano learning game.
KaraFun - KaraFun is the best online karaoke. Over 35,000 karaoke songs, with studio quality, at home or on the go. Regular updates. Free demo!
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.