Simply Piano - Fast and fun way to learn piano
Guitar Pro 7 - Create, play and share your tabs
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Yousician - Learn to play music at home, at your own pace
Synthesia - A fun way to learn how to play the piano.