Tinkersynth - Create and purchase unique generative art
Songstack - Swipe to discover new music for Spotify
Sampulator - Make (and record) beats on your keyboard
mixmello - mixmello is a free, open source tool to create remixed versions of your favourite playlists.
Splice Beat Maker - Make and share beats in your browser
Music Walker - Explore and play (via YouTube) songs similar to a seed song.