Guitaa is a free online music platform for musicians, that lets them find chords of any song of their choice on Guitar, Piano and Ukulele.
App:
La Touche Musicale allows you to learn the songs you love on piano. Connect your MIDI keyboard to your device and learn very quickly.
Perfect app for musicians
ChordU - Extracts chords from any song, integrated YouTube.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.
yalp.io - Automatic chords extraction from mp3 and YouTube
Synthesia - A fun way to learn how to play the piano.