Vivisimo is an engine that "auto-categorise" the search results from several other search engines. I don't know how but I don't care too much either. What I like about it is that it shows several categories of the search results; as opposed to Google where all returning items are listed one after another. When I search for Peter Bengtsson it then creates several categories such as "Zope", "Family", "Peterbe.com", etc. Some don't make sense but suppose a friend searches for "Peter Bengtsson" but is only interested my person stuff, or a Zope developer is interested in my stuff on Zope then this clustered search engine beats Google.
I also like the "preview" option that you see for each search result.
I was working with the engine in 2002. I'm rather sure that it does not classify the "web," just the top say 200 results.
But maybe they have changed somethings to make it work differently.