What are some alternatives?
When comparing Simply Piano and Touch Pianist, you can also consider the following products
Flowkey - The easiest way to learn piano with your iPhone or iPad
Pianu - Learn to play the piano in your browser.
Type Drummer - Drum by typing
Yousician - An interactive guitar-learning app.
lightnote - An interactive site to learn the basics of music theory 🎶
Playground Sessions - Online piano learning game.