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

A Lyft driver in San Francisco drops off a passenger as a taxi passes by. The smartphone app lets city dwellers hitch rides from strangers. Jeff Chiu/AP hide caption

itoggle caption Jeff Chiu/AP

Co-workers at Denver's Galvanize, a tech hub in Colorado's capital. Elise Hu/NPR hide caption

itoggle caption Elise Hu/NPR

Diners take part in the Herbal Remedy Picnic event, a meal arranged through food sharing site Feastly, in Washington, D.C. Jeff Wilkes hide caption

itoggle caption Jeff Wilkes

Napster founder Shawn Fanning in February 2001, after a ruling that the free Internet-based service must stop allowing copyrighted material to be shared. Paul Sakuma/AP hide caption

itoggle caption Paul Sakuma/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