Touch Pianist - Play piano like a pro without playing piano.
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
lightnote - An interactive site to learn the basics of music theory 🎶
Auricula - Practice your sense of hearing and learn to identify intervals for your musical development.
GNU Solfege - GNU Solfege is free music education software.