Meludia - Listening exercises and to sharpen your ear and music theory skills
Yousician - Learn to play music at home, at your own pace
GNU Solfege - GNU Solfege is free music education software.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Auricula - Practice your sense of hearing and learn to identify intervals for your musical development.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.