The increasingly popular “check-in” app foursquare was first introduced at SXSW 2009. And four years later, it was still one of the hottest apps at the Austin-hosted event.
With foursquare, which is available for iOS, Android, BlackBerry, and Windows Phone, you can post check-ins from any location or venue you visit to more easily meet up with friends. You can create personal "To Do" lists for specific venues, and post venue "Tips" for other users to see. Checking in at a specific location more than any other foursquare user over a 60-day period crowns you the “Mayor” of that location.
According to the foursquare founders Dennis Crowley and Naveen Selvadurai, 5 million people worldwide are using the app and over 1.5 billion check-ins are posted each day.