Moshe Safdie's 1967 Montreal Expo housing — 354 stacked-prefab concrete boxes producing 158 unique apartments.
From Wikipedia
Habitat 67, or just Habitat, is a housing complex at Cité du Havre, on the Saint Lawrence River, Montreal, Quebec, Canada, designed by Israeli-Canadian-American architect Moshe Safdie. It originated in his master's thesis at the School of Architecture at McGill University and then an amended version was built for Expo 67, a World's Fair held from April to October 1967. Its address is 2600 Avenue Pierre-Dupuy, next to the Marc-Drouin Quay. Habitat 67 is considered an architectural landmark and a recognized building in Montreal.