Playlist Machinery - Tools that help you create & organize your Spotify playlists
Poolsuite™ - The super-summer music player
Playlistor - Convert Apple Music playlists to Spotify and vice versa
Tiny Mix - NPR Tiny Desk — mixed up, one song at a time.
FreeYourMusic - Migrate from and to any music services
Magic Playlist - Get the playlist of your dreams based on a song