|Answer added on 9/11/2010: Foursquare|
Foursquare is a location-based social networking website, software for mobile devices. Users "check-in" at venues using a mobile website, text messaging or a device-specific application. They are then awarded points and sometimes "badges." The service was created in 2009 by Dennis Crowley and Naveen
Selvadurai; Crowley had previously founded the similar project Dodgeball, which Google bought in 2005 and shut down in 2009, replacing it with Google Latitude.