Meludia - Listening exercises and to sharpen your ear and music theory skills
GNU Solfege - GNU Solfege is free music education software.
Auricula - Practice your sense of hearing and learn to identify intervals for your musical development.
LenMus - LenMus is a free program for learning music.
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.