If you're looking to kill some time, have some fun and make some music all at the same time, Patatap is brilliant. It's a website that turns your browser into its own musical instrument. By hitting any letter from A-Z you can create all sorts of sounds and use all sorts of instruments. Every time you hit a letter a minimal visualisation appears on the screen. But when you hit the spacebar a whole new set of sounds and instruments come alive, the visualisations change too.
Embedded below is Patatap. Go ahead and give it a shot, it's great fun. Make sure to turn the volume up!