EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Touch Pianist - Play piano like a pro without playing piano.
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
Meludia - Listening exercises and to sharpen your ear and music theory skills
lightnote - An interactive site to learn the basics of music theory 🎶
Implied harmony website - Implied harmony website covers music theory basics.