A man picks up a rental car in in Burlingame, Calif., near San Francisco International Airport this summer. The car was left with the FlightCar company by a traveler who then flew out of the airport. Eric Risberg/AP hide caption

itoggle caption Eric Risberg/AP

Renting out your couches — or your entire place — is powered by San Francisco–based Airbnb, which has now connected more than half a million willing hosts and travelers in more than 34,000 cities. iStockphoto.com hide caption

itoggle caption iStockphoto.com