Spotalike - Spotify playlist with similar songs, according to Last.fm
Playlist Machinery - Tools that help you create & organize your Spotify playlists
MusaicFM - An iTunes like screen saver based on Spotify and Last.fm
Playlistor - Convert Apple Music playlists to Spotify and vice versa
Bowtie - Bowtie is a desktop accessory that allows you to see and control your music (iTunes, Spotify...
playAppleMusic.com - An (unofficial) web player for Apple Music