I guess Circles would have been more similar to Communites. There were also collections so you could post directly to a subprofile of your own about topics. For example here's one of the last screenshots I could find of my old collection on Bitcoin.

No one else could post top level on this like a community. It was just my posts that I self categorized into collections and then anyone could search my profile for my post collections to find my Bitcoin collection (or search collections for topics you were interested in.)