What are some alternatives?
When comparing Rocksmith and Simply Piano, you can also consider the following products
Clone Hero - Clone Hero is a free rhythm game, which can be played with any 5 or 6 button guitar controller...
Flowkey - The easiest way to learn piano with your iPhone or iPad
Frets on Fire - Bonus content.
Pianu - Learn to play the piano in your browser.
Osu - Osu is Music, Rhythm, Single and Multiplayer video game developed by Dean Herbert.
Yousician - An interactive guitar-learning app.