mixmello - mixmello is a free, open source tool to create remixed versions of your favourite playlists.
Songstack - Swipe to discover new music for Spotify
remixmonsta - Tired of Despacito? Find a cool remix instead
Remix - Solidity IDE (Integrated Development Environment)
Music Walker - Explore and play (via YouTube) songs similar to a seed song.
Google Music Lab - Interactive experiments that use the Web Audio API