I’ve begun to wonder about this question. There’s nothing implied in the existence of the fediverse that it will include every site, and there’s nothing implied in the existence of every non-fediverse site which would stop them from forming their own fediverse. One could technically say email providers have already achieved this, though this only really applies to email providers which doesn’t make it as useful as the fediverse we know and love. Are there actually other fediverses out there?
Pingback introduced back-linking websites practically forming a network in 2002.
URLs are a form of linking content, forming a network. Although uni-directional (into one direction only).
Some platforms integrate into websites and form a form of meta-network of their content or accounts.
Most recently and popular, the AT Protocol is an alternative generic protocol similar to the fediverse, powering Bluesky.
Web-rings were also a thing in the mid-to-late '90s before search engines really took off.
Basically you’d put a banner on your site that listed a site “before” yours in the ring, the one “after” and maybe a “random” link as well.
Wikipedia: https://en.wikipedia.org/wiki/Webring
Web ring sounds like a cam site for beople getting rimmed