What are some alternatives?
When comparing Songs2See and Playground Sessions, you can also consider the following products
Flowkey - The easiest way to learn piano with your iPhone or iPad
Synthesia - A fun way to learn how to play the piano.
Pianu - Learn to play the piano in your browser.
Simply Piano - Fast and fun way to learn piano
Yousician - An interactive guitar-learning app.
Skoove - Babbel for learning the piano