Foursquare is a social network based on geolocation for web and mobile devices. In addition to being a social network it is a game by which you can get points that become badges.
Users indicate where they are (Check-in) and give their opinions about the site.
Your Foursquare account should be linked to your Facebook and Twitter account.
Foursquare allows customer loyalty, they score points when they Check-in at your establishment and you can offer promotions to game winners.
Take advantage of smartphone generation, loyalty to your customers.