is a great app to learn to play the piano. It is compatible with a range of keyboards and has an excellent learning method. It's suitable for all ages and every level of experience. If you don't have a piano, no worries. This app includes a touch keyboard so you can practice on your phone. There's a free version and an advanced paid version.
You can start with Music Theory lessons and you'll also learn to reach sheet music. This app guides you step by step as you develop your skills. It also has a sound recognition system that evaluates you as you play. For this simply place your mobile device near the piano and it will recognize the notes you play in order to guide your learning.
Simply Piano is also available for iPhone here