MisterJack - Make and share playlists
Parallel - Listen to music with friends over Spotify at the same time
Designers MX - Curated playlists by designers, for designers.
Slackbox - Spotify playlist collaboration through Slack
Monolist.co - The command center for engineers. Tasks, pull requests, messages, docs — all in one place
TuneMeet - Chat with people who are listening to the same song