Stalqer, which is similar to another , tracks a user's location and the location of their friends, allowing them to see where each other are.
One key difference between Stalqer and Foursquare is that Stalqer updates the user's location without them actually opening up the app. Foursquare requires the user to have the app open.
Stalqer facilitates the location updates by setting up an email account that operates in the iPhone's background. When the phone checks for mail, the app is fed a location point, which happens by default every 15 minutes.
In addition to background functionality, Stalqer lets users import their Facebook friends, via Facebook Connect, to the app. If a user's friends have made their general location public via Facebook, the app then syncs their friends with the user's iPhone contacts and will then show them where their friends are.
Users can see their friends' locations via a list format or on a map. They can choose to turn the app on or off or report different levels of data to different groups. For example, users can make sure the app only shows the city they're in as opposed to their exact location within that city.
The app also has close to half a million bars and restaurants listed in the US.
Stalqer intends to expand the app into non-US locations in the future.