Try Yousician. It's an app for learning the guitar (I think they are working on adding the piano lessons). There are some theory lessons with practice sessions.

Try Yousician. It's an app for learning the guitar (I think they are working on adding the piano lessons). There are some theory lessons with practice sessions. I tried learning the guitar by tabs and accords of the songs I liked, but did not get too far. Yousician shows a clear skill progression (easy melodies->hard melodies) and provides some foundation for further learning and improvement. If only I had more time to practice :)