Spacetime Watch

A watch face with a map that rotates counterclockwise every 24 hours, like the Earth does when seen from the north, making it possible to see roughly what time it is everywhere on Earth at once. It also has an accurate sky map overlay.

There's a full explanation on the website, with interactive visualizations. It is highly recommended to take a look, to learn how to read the watch face properly: https://spacetime.watch/