Spotify - Map shows when two people play same song at same time
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
SOUNDS - Discover music with friends
muted.io - A magical collection of interactive music theory tools & visual reference pages for musicians and music producers
Songlink - Share music with anyone.
soundrop - Soundrop is an app that allows you to create your own personalized sound track to keep you focused or relax.