AirBnB

AirBnB

Entrepreneurs: Joe Gebbia, 27, Nathan Blecharczyk, 25 and Brian Chesky, 27

Funding: Seed funding from Y-Combinator; otherwise, self-funded

In 2007, on the occasion of the annual Industrial Design Society of America conference, every one of San Francisco's hotels was sold out. So roommates Joe Gebbia and Brian Chesky opted to rent space in their apartment to three strangers planning to attend the conference. Gebbia and Chesky soon learned that a lot more people were willing to rent out space, too. Joined by Web-savvy friend Nathan Blecharczyk, they built a site that would match people with extra living space with travelers willing to pay for it. The site now lists lodgings for rent, ranging from couches and spare rooms to entire homes, in 830 cities in 73 countries.

Lessons learned: "People are willing to try new things to save money, and they're willing to be resourceful," Chesky says.