Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Simply Piano - Fast and fun way to learn piano
Yousician - Learn to play music at home, at your own pace
Jameasy for Violin - Play rhythm game with a real violin. you can play with background music and real-time feedback
alphaTab - alphaTab is a cross platform music notation and guitar tablature rendering library.
Synthesia - A fun way to learn how to play the piano.