What are some alternatives?
When comparing Cloud Piano and Simply Piano, you can also consider the following products
Piano Companion - Chord & scale dictionary with libraries, reverse mode, etc.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Touch Pianist - Play piano like a pro without playing piano.
Pianu - Learn to play the piano in your browser.
Touch Bar Piano - Play piano on the new MacBook Pro's Touch Bar 🎹
Yousician - An interactive guitar-learning app.