I recall, circa 2000, a project that I can't name at the moment that I toyed with in college that had this concept. You could host your own area and connect it to other areas hosted by other people. The name "Metaverse" is in my head, but googling it (quick search, probably missed something) was dominated by Stephenson's concept from Snow Crash and not a software project by that name.
> You could host your own area and connect it to other areas hosted by other people.
Sounds like Croquet/OpenCobalt/Qwaq/Teleplace/Terf (hooray for forks!). Different spaces can be hosted by anyone, like Web pages, and the hyperlink equivalent is a 'portal' which you can step through to go from one "world" to another.
As far as I understand it, the client processes the world via a stream of events, which a p2p protocol tries to keep consistent between all of the clients (e.g. user avatars) inhabiting a world. Going through a 'portal' switches your client to the another "world", and hence another event stream, so there's no central authority.
See https://en.wikipedia.org/wiki/Open_Cobalt for example.
Edit: It seems to be p2p, rather than server-based, according to:
> The Open Cobalt application leverages peer-based messaging to eliminate the need for virtual world servers/commercial services and makes it very simple for end-users to create and securely share deeply collaborative virtual worlds that run on all major software operating systems.