Playlist Machinery - Tools that help you create & organize your Spotify playlists
Undrtone - Social layer on top of Spotify and Rdio from Scott Vener
Playlistor - Convert Apple Music playlists to Spotify and vice versa
PlaylistMap - Connect with Spotify playlist curators from around the world
FreeYourMusic - Migrate from and to any music services
BeatSense - Discover great music hand-picked by real people, in a single click. FREE and in real-time!