Foursquare is an application that allows you to stay up to date about the places your friends recommend to you.
The main advantage it gives is that you can know what places your friends recommend, but also you can learn tricks or make sure you don't miss anything thanks to the messages that the rest of the sites visitors leave.
You can compete with your friends in a type of game, where you count the number of visits, the number of different places visited and the frequency of the visits. All of these statistics are visible form your profile.
Also, Foursquare now allows you to take advantage of special offers given by business owners just for recommending places to their friends.
