EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
GNU Solfege - GNU Solfege is free music education software.
Perfect Ear - A simple yet advanced application for improving your solfege skills.
KDE Minuet - Free music education software, thoughtfully designed to push your musical skills to the next level.
Jalmus - Online guide to compare all musical instruments : keyboards (MIDI controller, Synthesizer, Stage Piano, Digital Piano …), guitars, basses, (...)
Auricula - Practice your sense of hearing and learn to identify intervals for your musical development.