mixmello - mixmello is a free, open source tool to create remixed versions of your favourite playlists.
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
remixmonsta - Tired of Despacito? Find a cool remix instead
Musicroamer - A visual Pandora for discovering new music
The Rick Astley Remixer - Remix your favourite songs in your browser.
stats.fm - With the click of a button you'll be logged with your Spotify account and you'll instantly gain access to a valhalla of cool stats and insights.