Small Demons is an upcoming website that looks to catalog the world inside books—you can find every novel that contains a reference to Abraham Lincoln, say, or any novel that mentions gelato. This video, which I found on Galleycat, explains it pretty well:

This is another concept from Richard Nash—read my introduction to Red Lemonade right here—and it's a good one. Nash is a firm believer that tags are one of the most important innovations of the internet age, and a comprehensive tagged encyclopedia of books with a smooth interface and lots of little social media treasures tucked away inside the experience could be a great way to apply tags to books.