Slackbox - Spotify playlist collaboration through Slack
BeatSense - Discover great music hand-picked by real people, in a single click. FREE and in real-time!
Partyhero - Pass your friends the aux!
Twinjack - Stream Spotify music with anyone with just a link
Songmash - Create playlists with music that you and your friends love
ReverbNation Discover - Stream hand-picked, ad free music from emerging artists.