Flowkey - The easiest way to learn piano with your iPhone or iPad
Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
Yousician - Learn to play music at home, at your own pace
GNUitar - GNUitar is guitar effects software that allows you to use your PC as guitar processor.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.