Continuing on your suggestion.

There could be open source tooling to create custom private "closednets", with

- trust ring mechanism to allow invitations, flagging, banning, and banning those that invite people who were banned

- the rules of the closednet

- search engine with opt-in scraping

- portal (remember the 80s?) with all the registered nodes, perhaps by service category such as public git repo hosts, web sites etc.

etc.

The first closednet could be Hacker News.

It doesn't have to be an IP-layer network. A website that you need to log in to view works just as well.