Rulers of the Past
A synchronic atlas of world rulers — who held power, anywhere in the world, at the same moment in time, from antiquity to the 18th century.
Most lists of rulers run down a single throne. This one runs across: pick a year and see who was in power everywhere at once — the emperor in Rome, the dynasty in China, the king in a European fragment — laid side by side on one synchronic timeline.
It is assembled from Wikipedia and Wikidata and covers antiquity through the 18th century. The same engine drives the focused sibling editions for Ancient Rome and Ancient Egypt.