Officially launched on February 5th, 2006, Prosper.com is the U.S. sister site of London, U.K. based Zopa.com. Prosper can be defined as a Social Lending Marketplace.
A snippet from the Techcrunch Review:
It generally takes 2-4 days to close a loan, according to Prosper. However, a borrower can request an expedited loan, which will take the first lenders who meet the minimum requirements for amount and interest rate.