EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Captain Chords - Write chord progressions in your favorite DAW
lightnote - An interactive site to learn the basics of music theory 🎶
Odesi - ODESI is a music sketchpad that exports your projects to Audio and MIDI.
Meludia - Listening exercises and to sharpen your ear and music theory skills
Cthulhu - VST MIDI-FX plugin for harmonic inspiration