Heartbeat - Listen to music with your friends together, on Spotify
Discover on Demand - Just like Spotify's Discover Weekly, but whenever you want.
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Rocketgraph - Rocketgraph is an open-source drop in replacement to Firebase, except it's much better.
Join My Playlist - Listen to music live together with your friends in Spotify.
Spotify - Map shows when two people play same song at same time