Spotalike - Spotify playlist with similar songs, according to Last.fm
Slackbox - Spotify playlist collaboration through Slack
MusaicFM - An iTunes like screen saver based on Spotify and Last.fm
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...
Exportify - Export your playlists from Spotify