This one crossed the transom just a little too late for this morning's post, but I didn't want it to wait another week. The author of Not in WorldCat describes the blog as "an outlet for one bookseller/librarian (me) to feature unusual, rare and interesting items that exist outside of WorldCat’s vast reach." Basically it's photos and descriptions of books for sale on ABE that don't have entries in WorldCat (or didn't when the booksellers wrote up the descriptions, at least).
I've added a sidebar link.
[h/t The Little Professor, Cliopatria]