Simply Piano - Fast and fun way to learn piano
EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
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.