TubeLister - Generate a YouTube playlist from your opened tabs.
Playlist Machinery - Tools that help you create & organize your Spotify playlists
DiskyT - Youtube playlists done right
Playlistor - Convert Apple Music playlists to Spotify and vice versa
OrganizeTube - Create video playlists from Youtube, Vimeo and other sources
Tune My Music - Transfer Playlists Between Music Services