Heartbeat - Listen to music with your friends together, on Spotify
Parallel - Listen to music with friends over Spotify at the same time
Slackbox - Spotify playlist collaboration through Slack
Join My Playlist - Listen to music live together with your friends in Spotify.
aux.app - A free web-based music platform to play music from other popular online streaming services.
TuneMeet - Chat with people who are listening to the same song