I suggest "quad." Yes, the term is traditionally associated with university campuses, but "campus" has expanded to non-academic settings, such as Googleplex and Apple Campus.
Kids are playing in the quad.
Where did you park the car? In the quad.
"Communal" sounds odd as a noun. "Common" (or Commons) could work. Think "Boston Common." But like plaza and square, "common" has a more public meaning, but that may be appropriate for a Russian/Soviet application.
noun
Often16. Often, commons. Chiefly New England. a tract of land owned or used jointly by the residents of a community, usually a central square or park in a city or town.
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