Use Extensions to Build Foursquare into Your Site
This location-based service is the one whose game-like interface has been copied by the competition. Foursquare has shot to the front of the pack with its combination of antic humor and growing usefulness. Users compete with their friends to see who can check in most often, and they're rewarded with weekly bragging rights on public leaderboards that show who visited the most places and earned the most points.
Many mobile websites have already integrated Foursquare. Navigate to the Foursquare apps gallery, and click the Websites tab to see examples of mobile websites using the GPS and personal data generated by Foursquare on their sites.
One example is Citynumbers.com, which shows what the most popular events, concerts, or restaurants are in Amsterdam, according to how many users are checking in (and saying favorable things) using Foursquare. Other mobile websites let you see where in your city the highest number of users are congregating, the hottest event, or the location where your friends in the area want to meet for lunch, based on a group vote.