EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Ocean beta - Make music with friends in your browser
GNU Solfege - GNU Solfege is free music education software.
iO-808 - Rhythm composer modeled after Roland's TR-808 drum machine.
Meludia - Listening exercises and to sharpen your ear and music theory skills
Cameo - Book personalized video shoutouts from your favorite people