Jukebox - Collaborative music player
Shared Spotify - Find the common songs you have between friends
OutLoud Social Jukebox - Control the music with your friends in real-time
Spotify Codes - Share codes for songs, artists, and playlists from Spotify
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Bands on a Budget - Economical SWAG meant for bands, often hijacked by startups