Simply Piano - Fast and fun way to learn piano
Meludia - Listening exercises and to sharpen your ear and music theory skills
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
GNU Solfege - GNU Solfege is free music education software.
Yousician - Learn to play music at home, at your own pace
Perfect Ear - A simple yet advanced application for improving your solfege skills.