Foursquare is a free mobile app that helps users keep up and meet up with friends. Since 2009, more than 45 million people have joined Foursquare, checking in around the world over 5 billion times. Those check-ins power the Foursquare Explore search engine, which provides personalized recommendations of the best places nearby.
In addition, more than 1.6 million businesses from large brands to small merchants have used its advertising and merchant tools to attract and maintain customers. More than 50,000 developers use the Foursquare API to add location to their apps. It has applications for iPhone, Android, BlackBerry, Windows Phone, Nokia S40/Asha, and Symbian.