KnowItAll
Let’s see if I’ve got this right - KnowItAll, out of the University of Washinton is a search engine that concentrates on extracting lists out of search results:
There’s a short New Scientist article on it too:
Search engine tackles tricky lists
Is it open source? I don’t know! Although it does or will incorporate Nutch software and shares at least one contributor, nothing indicates it is intended to be open source.