Black Hole Finder

Citizens worldwide can now help identify newly formed black holes, contributing to groundbreaking astronomical research.

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.