APIs are a very important factor in the growth of social networks. They provide a set of procedures which developers all around the world can use to improve features, to make new applications, new graphic styles, to mash up with other social networks or to make social network working on different kind of devices. If a social network is a house, its APIs are the doors: they tell the developer how to enter. There are APIs for registration, authentication, posting a comment, seeing the list of friends and, in general, all the allowed operations. Social network provides documentation about its APIs to let the developers make applications.

Several applications have been developed for foursquare using APIs and they are available at foursquare.com/apps/. Their most important aspect is that they focus on social interaction. In particular, there are several applications for meeting new people. Gatsby, for example, is an application which introduces you to nearby people who share your interests. It could suggest you meeting a user 400 meters far because you both love cats or, if you like running, going to the park because there is a group of people who like it too.

Singles for Foursquare is a very attractive application which lets you view and chat with singles who are close to you. It could have a very fast growth, especially between young users.

Besides applications to meet new people, Friends Around is an application designed to meet friends around you and stay connected with them. Moreover, it allows sharing across other social networks like Facebook and Twitter. Mashing up with other social networks, especially Facebook, the most famous one, is a choice often taken by foursquare. And, in fact, several applications have been developed appropriately for this purpose. Footfeed, for example, is the first native iPhone application that makes it easy to check-in to Brightkite, foursquare and Gowalla simultaneously without the need to open multiple applications. More sophisticated applications, like TwentyThree, Myallo HotList and GeoLorean also let you see your friends on a radar map, where you can find the venues, too. TwentyThree, in particular, merges contacts recognized as identical and identical venues found on different networks. The aim is to give you the sensation of being connected to an only higher level social network.

But the strongest applications are designed to merge people who share the same interests. RunnersUnite!, for example, lets you invite your friends to run with you, find close popular running spots and find people who are running around you. Moreover, users who install this application will be able to receive special promotions from Dick’s Sporting Goods.

Shakedown, instead, is an application designed just for Shake Shack line, a roadside burger stand

The possible applications for categories of users are countless. An application could be designed, for example, for people who love cinema. They would have the possibility to find the shows to attend, buy the tickets, see what people say about a film, see who has bought the ticket for a show, meet new people who like the same film. Another application could be designed for McDonald’s chain. People would have the possibility to meet other people who like the same burger, see how many people there are in a particular moment in all the McDonald’s shops and so on. This kind of applications can create lots of networks inside the whole network.

foursquare also takes care of important events. map.pr, for example, is an application designed expressly for the World Cup in South Africa. It lets users find on a map foursquare venues in the city there the matches take part and allows do check-ins as fun of a team, creating groups inside the users of the application. And it lets post to other social networks too.

There are also several applications which improve the basic features of foursquare. PhiSq scanner, for example, lets check-in just by scanning a barcode. It is one of the few applications which don’t have effects on social interaction, but it is very useful anyway

foursquare’s strategy derives from the common aspects of most of the applications. Their aim is to create a significant customer base. After that, the word of mouth will do the rest, as happened for Facebook. This strategy is focused on innovation and social interaction. Innovation is achieved thanks to new features, like multimedia check-in, or completely new applications, like Fourcash. Social interaction is followed in three ways. Firstly, giving the user the possibility to meet new people, with applications like Meet Gatsby and Singles for Foursquare. Secondly, creating groups of users who share the same interests, like RunnersUnite!, or who are interested in a particular event, like map.pr. Finally, mashing up with other social networks. This last aspect, in particular, is very important in the first years of life of a social network, because it is a way to get inside other strong social networks and exploit their strong word of mouth. Imagine the potential of entering the Facebook system, with its half billion of users.

Taking care to the design and update of APIs is very important, because only thanks to well designed APIs it is possible to develop such a countless number of applications. Considering the importance of mash up applications, it takes importance the concept of API adapter. It is an intermediate level between different APIs which let them communicate each other. Providing the developers a set of intermediate procedures to link different social networks will make their work easier and will reduce the probability of mistakes. Suppose a developer wants to create an application to link foursquare to Facebook. If he owns this set of intermediate procedures he has to concentrate only on new features and graphical aspects.