Guitar - Git GUI Client. Open Source, Free Software (GPL v2). Run on Windows, macOS and Linux.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Upwork - Forget the old rules. You can have the best people. Right now. Right here.
Yousician - Learn to play music at home, at your own pace
White Tiles 4 - White Tiles 4 is a music game that allows you to enjoy your leisure time by transforming your device into a floating piano.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.