Some of these apps are primarily on Facebook but others interact with mobile apps from the same publisher. For example, if someone downloads Foodspotting to their smart phone and takes a picture or rates a meal they're having at a restaurant, that picture and rating can immediately appear on their Facebook Timeline. Travelers can add the Gogobot and TripAdvisor apps to bring a virtual passport to their timeline, and show their friends where they've been and share tips about their favorite spots from around the world. Rotten Tomatoes allows users to share their thoughts on movies they've watched and learn about what their friends are watching.
All this is possible thanks to Facebook "open graph," which is a set of application interface tools (APIs) that allows developers to create apps that share user activities back to Facebook.
Users are required to authorize the application and determine who they want to share with. Even after they start sharing they have access to controls that let them limit the audience further.
Facebook, tipped for a $100bn initial public offering, is looking for new ways to get people to spend more time on the site - which will attract more advertising.