What are some alternatives?
When comparing GetHarmony.net and Amazing Slow Downer, you can also consider the following products
yalp.io - Automatic chords extraction from mp3 and YouTube
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
Sonic Visualiser - Sonic Visualiser is a program for viewing and analysing the contents of music audio files.
GUITAA - Turn ANY song into chords, play along with interactive chords and diagram, transpose, loop, tempo control.
ChordU - Extracts chords from any song, integrated YouTube.
Chord Generator - Used to draw guitar chord images.