The Soviets had an “apartment swap” system for people who wanted to move around filled-to-capacity neighborhoods. You would get on the list with where you currently lived and put in where you wanted to move and would get informed when there was a match. Sometimes matches would be arranged in triangles or other more complex shapes, but since everybody involved needed to get on the same page this was rare. The wait to move depended on how lucky you were - sometimes you’d get a match right away, sometimes you’d forget about it until ten years later when you would get a letter asking if you were still interested.

This was all in the 60s and 70s when things were generally more chill.