EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Meludia - Listening exercises and to sharpen your ear and music theory skills
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
Ear Teacher - Ear Teacher is a music theory and ear training application.
lightnote - An interactive site to learn the basics of music theory 🎶
GNU Solfege - GNU Solfege is free music education software.