What are some alternatives?
When comparing Pianu and Jameasy for Violin, you can also consider the following products
Synthesia - A fun way to learn how to play the piano.
Simply Piano - Fast and fun way to learn piano
Yousician - An interactive guitar-learning app.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Playground Sessions - Online piano learning game.
alphaTab - alphaTab is a cross platform music notation and guitar tablature rendering library.