What are some alternatives?
When comparing Pianu and Playground Sessions, you can also consider the following products
Synthesia - A fun way to learn how to play the piano.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Simply Piano - Fast and fun way to learn piano
Skoove - Babbel for learning the piano
Yousician - An interactive guitar-learning app.
Piano Marvel - Online Platform to interactively learn Piano and Drums on your own or with a real Teacher.