Their four-year-old microfinance site redefined giving by persuading individuals to lend as little as $25 to small businesses in the developing world and today in the U.S.; Kiva's 574,000 citizen lenders have since lent $96 million. Flannery was a programmer at Tivo, Shah a product manager at PayPal. They're now the "it" boys for philanthropy 2.0. (Flannery's ex-wife, Jessica Jackley, a co-founder, has moved on.)

Latest move: a deal to have Moody's rate Kiva's microfinance partners.

Shared mentor: LinkedIn founder Reid Hoffman.

influential, interesting, 40 under 40 (2009),