Playlistful - Collaborative playlists for parties!
22tracks - DJ curated Spotify playlists on iOS
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Spotify - Map shows when two people play same song at same time
klaep - music collaboration - klaep is a social music collaboration network for musicians
Yeloha - Airbnb for solar power