People in the past have mentioned making things with pureed beans (and
named them beanut butter)
Also, I've purchased canned chestnut (a.k.a marron) puree which I
think is low in fat. I don't think you'd want to make a sandwich from
the puree but people do eat it straight. There are some recipes in
Alice Medrich's "Chocolate and the Art of Low-Fat Desserts" that call
for chesnut puree. (Great book, but I have to mention that Medrich's
concept of lowfat is not quite the same as this list's definition of
lowfat. It's all relative. Medrich once ran a California bakery named
Cocolat.)
Chestnut puree is pretty pricey and comes sweetened or unsweetened
(usually in a gourmet shop or a well-stocked grocery). I think I once
saw a recipe in an epicurious.com forum archive for making puree from
chestnuts.
Unfortunately, neither of these really taste exactly like peanuts.
jayne