Came across this site today as a result of a Globe and Mail article. It's basically a website that tries to catalogue all the little details of books and cross-catalogue them - so for example, you could find out any book that mentions or features Greta Garbo, or a particular street in Edinburgh, or whatever. But it also means you can detail check small elements of any book in their database - and add details for books if they're not in there already.
I think this could be an amazing resource for fanfic writers, and probably academics too... I just made an account!