Flowkey - The easiest way to learn piano with your iPhone or iPad
Fachords - Fachords is an online site that provides many resources that you can use to take your guitar skills to the next level.
Jameasy for Violin - Play rhythm game with a real violin. you can play with background music and real-time feedback
TrueFire - The Best Guitar Lessons Online Fast. Easy. Fun.
alphaTab - alphaTab is a cross platform music notation and guitar tablature rendering library.
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.