My experience/opinion is that a circles-based approach is a usability nightmare since relationships are fluid and fuzzy, so Haven only has one "share group"--everyone with access to your Haven. That said, it's all built on open protocols (RSS), so it would be pretty straightforward for someone to fork it or build their own that implemented a circles-style approach to sharing.
[1]: https://havenweb.org
Some of the work we did then still exists today in various forms. Activity Steams led to Activity Pub, which has seen far more adoption than we ever did.
And microformats are still widely used in some communities, though certainly not like it could have been, largely things to Google putting weight behind schema.org. For example, nearly all of the indieweb.org work is based around microformats at the core, with things like webmention, micropub, etc
Perhaps a better answer to that question is "the Fediverse", which is based on ActivityPub. Unfortunately, though, there still seem to be open questions about how well/widely the Fediverse supports something like "circles" (the concept that Google Plus had) for selectively sharing content with different groups of people.
[0] http://microformats.org/wiki/h-card
[1] https://rusingh.com/fediverse-google-plus-circles/