EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
ChordU - Extracts chords from any song, integrated YouTube.
GNU Solfege - GNU Solfege is free music education software.
Guitaa.com - Turn ANY song into chords, play along with interactive chords and diagram, transpose, loop, tempo control.
Perfect Ear - A simple yet advanced application for improving your solfege skills.
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.