Thread:Extension talk:Simple Farm/Great extension/reply

That is right. It's not the only extension like that, there are at least two more, see Category:Wiki farm. Extension:WikiFarm though seems to have documentation in Russian only and Extension:Farmer requires changes on the MW code, also it has been reported broken quite often. Just read the documentation of Simple Farm and then you still need to use some rewrite rules on your web server, so all web-requests to the particular wikis are getting re-directed to the one MediaWiki installation with Simple Farm inside.