Agents of up to 8 q.d colours live on a grid with some empty cells. An agent stays put if at least τ of its occupied neighbours share its colour; otherwise it moves to a random empty cell. The seed picks τ and the number of colours.
Tap to shuffle a patch. The same ?seed= always gives the same run.
LITSchelling’s model (1971). Each colour’s count is conserved, or the page throws.
WALLA model of a mechanism, not a description of any real city.