Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
AMPLI.FI - Live online music community. Twitch for tunes.
muted.io - A magical collection of interactive music theory tools & visual reference pages for musicians and music producers
Krue - Twitch for music: live streams from amazing musicians
soundrop - Soundrop is an app that allows you to create your own personalized sound track to keep you focused or relax.
Soundscape - Sync your music with the open source community