Mediachest — like eBay, except you borrow instead of buy

Michael sez: "Mediachest is a social software site that allows users to inventory their collection of physical media items and search the collections of their friends and friends-of-friends for items such as DVDs or books that they would like to borrow. The site facilitates the borrowing and loaning of these items in a similar way to how Ebay facilitates online auctions — there are user profiles, feedback pages, and rankings. In addition to searching the collections of friends you are able to see the items of people that are geographically close to you, or that are members of groups that you associate with (such as a student organization, gym, or work place group)."
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