Heartbeat - Listen to music with your friends together, on Spotify
Youtube-DJ - Mix YouTube songs together
Partyhero - Pass your friends the aux!
Edjing - Discover edjing and edjing Pro, the most powerful DJ apps for music lovers! Mix on Android, Windows and iOS devices and record then share your DJ sets!
Slackbox - Spotify playlist collaboration through Slack
YOU.DJ - Mix SoundCloud music and Youtube videos live in your browser.