Heartbeat - Listen to music with your friends together, on Spotify
Magic Playlist - Get the playlist of your dreams based on a song
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Spotalike - Spotify playlist with similar songs, according to Last.fm
Join My Playlist - Listen to music live together with your friends in Spotify.
Playlist Machinery - Tools that help you create & organize your Spotify playlists