The idea behind Prosper is a bit unusual today, but, as the site reminds readers, person-to-person lending — loans without a financial intermediary — has been around since 300 A.D. For those more used to the Internet age, think of it as eBay meets your neighborhood bank. Prosper is an online marketplace that allows lenders and borrowers to bid for loans — with fees and rates than can be much lower than those of a lending institution. Prosper uses credit scores to help its users gauge the risks of their deals, and easy-to-follow instructions on the site help clarify the details.