Slackbox - Spotify playlist collaboration through Slack
Replayify - Create playlists from your most played Spotify tracks
Partyhero - Pass your friends the aux!
SpotiMy - Play/Pause and Next/Previous functions for Spotify directly on your Menu Bar!
Songmash - Create playlists with music that you and your friends love
Muzzy - it’s a tiny and gorgeous iTunes companion that lives on your menu bar. For Mac OSX, its free!