As per the title really.
When I've time I love a little random browse around online but often end up just looking at the same old things.
So post your interesting or unusual sites that you're recommend here with a small description to help readers decide if it would be of interest. Hopefully we can build a dossier of some fun sites!

I'll start with a fun time-waster.

https://quickdraw.withgoogle.com/

It tells you what to draw in 20 seconds and an AI bot tries to guess as you draw in real-time. 6 drawings per round - it's tougher than you think to get the bot to correctly guess all 6!