EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Touch Pianist - Play piano like a pro without playing piano.
Meludia - Listening exercises and to sharpen your ear and music theory skills
GNU Solfege - GNU Solfege is free music education software.
lightnote - An interactive site to learn the basics of music theory 🎶
Perfect Ear - A simple yet advanced application for improving your solfege skills.