Book Exchange/Library?

I was trying to find out the URL for a project that I read about a month ago in a magazine but I forgot to write it down. I am searching all over the palce and I can't find it.

It is a online book exchange were people who want to give away thier books log on to the site, enter where they will drop off the book they have, lets say leaving it in a grocery store behind the canned peas, and then print out a label to put inside the book that they have particapated in the project, just in case some one else finds the book.

Sounds like a great project but I can't find the site. ANy help would be great.

Stephan