Jukebox - Collaborative music player
Magic Playlist - Get the playlist of your dreams based on a song
Musify - Enjoy your favorite songs, listen unlimited mp3 and play musics.
Spotalike - Spotify playlist with similar songs, according to Last.fm
ZenPen - A minimalist writing zone, where you can block out all distractions and get to what's important.
Playlist Machinery - Tools that help you create & organize your Spotify playlists