Fachords - Fachords is an online site that provides many resources that you can use to take your guitar skills to the next level.
Flowkey - The easiest way to learn piano with your iPhone or iPad
TrueFire - The Best Guitar Lessons Online Fast. Easy. Fun.
Yousician - Learn to play music at home, at your own pace
Gitarrero Beginner - Gitarrero Beginner is a multi-featured, and easy-to-use guitar school developed as a guide to help you learn guitar skills and play them comfortably.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.