Wikis are essentially this, but aren’t often thought of as such. Example: Wikipedia with talk pages are roughly this but on a broader scale. I’m not aware of many truly collaborative commonplace books which might allow for networked thinking this way. There are a few silo examples I can think of like @observablehq which are collaborative digital notebooks. @AREdotNA will allow something like this as well.
The internet is sort of what you’re looking for too. The interactivity, distillation, and UI is missing/broken in places and not well distributed yet. It would be great if there were more crosslinking/backlinking visible, perhaps the Webmention spec and display of backlinks across the web would make this more apparent.
The best example I can think of on a particular scale is what the IndieWeb community is doing on their own individual websites, in combination with a chat channel, newsletter, news hub, and collaborative documentation with the best pieces showing up distilled into something more coherent on their wiki. Their multi-modal platforms allow small-scale conversation, experimentation, collaboration, and larger scale aggregation.
I leverage a bit of this with my own site which collects copies of everything I post to the IndieWeb wiki (via PESOS using IFTTT->webhook->Micropub). I also get notifications from the wiki via the same process when anyone edits a page on which I’m mentioned. In this case I actively am using my commonplace book to talk with the IndieWeb’s commonplace book (a wiki), which incidentally has Webmentions though they’re not being displayed (yet).
There are a few Reddit-like community aggregation hubs that use Webmention for potential conversation/cross collaboration/discovery. These include:
But they’re not being used as heavily for the networking directly in their place, but between websites run individually.
@CJEller3 has an interesting and clever smaller-scale example I saw recently: https://blog.cjeller.site/talking-with-blocks. Scaling his idea up into a broader community would be interesting.
I suppose that there’s no reason that one couldn’t have a multiuser CMS platform (WordPress MU?) that did this for people individually as well as for allowing a broader community. Greg McVerry and I have batted the idea of having either newspapers/magazines or public libraries host IndieWeb-as-a-Service platforms for their communities.
Your question is a good one; I’m hoping we’ll get there eventually.