ChordU - Extracts chords from any song, integrated YouTube.
Guitaa.com - Turn ANY song into chords, play along with interactive chords and diagram, transpose, loop, tempo control.
Tune Transcriber - Learn and transcribe music for free from your web browser (no install needed).
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
Amazing Slow Downer - !A slow down music software for Mac and Windows computers - Amazing Slow Downer
Riffstation - The web version is Free and you can learn how to play Chords with Youtube Songs.