Is My Blue Your Blue?

A color naming test designed to measure your personal blue-green boundary.

ileftmystuff.com

You might have some luck with this service if you leave something behind in a hotel.

onlyvisitonce.com

Read some advice, leave some advice. But you can only visit the site once.

Air Quality Stripes

Shows the concentration of particulate matter air pollution (PM2.5) in cities around the world.