Trading Places

Foursquare
New York
Location-based mobile apps combining social networking and gaming
Co-founder and CEO: Dennis Crowley

Foursquare is a popular online and mobile service that lets people "check in" and report their location to find friends or get tips about the place they're visiting. The company uses game mechanics to reward users and grants "mayorships" for being a venue's most frequent visitor. Tens of thousands of merchants around the world are experimenting with special offers to Foursquare users. The company has around 3 million users, with some 40 percent of its traffic coming from outside the U.S.