Unithrive is a non-profits that allows alumni to help students by granting interest-free loans. Currently only alumni and students of Harvard can sign up, but Unithrive plans to expand to other schools in fall 2009.
Students can borrow between 500 and 2,000 US$ per semester. Repayment begins after they graduate.
The founders Joshua Kushner, Nimay Metha and Tanuj Parikh recently graduated from Harvard. For more on Unithrive read this recent New York Times article.