Parallel - Listen to music with friends over Spotify at the same time
BeatMix - Enables Shuffle and Radio for multiple artists in Spotify
Slackbox - Spotify playlist collaboration through Slack
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Join My Playlist - Listen to music live together with your friends in Spotify.
TuneMeet - Chat with people who are listening to the same song