This is a simulation of the world-famous Prague Astronomical Clock (Pražský Orloj), a medieval astronomical clock first installed in 1410, and still running today (with periods of disrepair and various renovations over that span of time).
The real, physical clock is designed to run at the particular latitude of Prague, which is about 50°N. This simulator, however, can be set for any location on Earth, and you can either show the current time, or set a particular time to see how that time would be displayed.
The positioning of the simulator’s clock hands, hour dial, sun, moon, and ecliptic wheel are by default done using your computer’s clock and modern astronomical calculations, but mechanical clock timing can also be approximately simulated.
The original SVG clock graphics and font used here were originally developed by Jan Tošovský, as found on this website.