Each time that I've tried one of these services, I find myself trying to convince my friends to use it so that I can have meaningful contacts to keep track of. Some of them don't have the right phone, or are worried about blasting out their GPS coordinates to the world.
Stalqer, available as a free iPhone app since earlier this month, has solved this problem by connecting to your Facebook, Twitter and Foursquare accounts and providing a map of your friends based on information it gathers from those services, even if they don't use Stalqer.
If your friend uses a geo-tagged Tweet, or if they check in on Foursquare, Stalqer knows where they are. Stalqer can even pull your friends' location from their Facebook profiles if they publicly display that information, but in most cases this is limited to the city level.
You can also view your friends' locations in a list, or even in an augmented reality view by turning the phone on its side while in the map view, but Stalqer's killer feature is its workaround of a pesky iPhone limitation.
Since iPhones lack the ability to run applications in the background, Stalqer piggybacks their service on one of the phone's core services with periodic updates. By cleverly monitoring the data exchange on your iPhone when the Mail app checks for new messages, Stalqer can update your location as often as your phone checks for email.
After running Stalqer's custom mail settings configuration tool, I took the app on a test drive, and sure enough, there I was moving along the map with each check of my email.
Not only is this an innovative iPhone workaround, it's an interesting way to increase check ins without games, badges or rewards like those found in Foursquare.
The San Francisco-based company appears to understand that forcing users to create yet another online account would limit the app's potential, so instead, you log in immediately through Facebook Connect. In this sense, Stalqer isn't trying to become another popular social network - it wants to be the aggregator of your friends' locations.
The app provides push notifications for nearby friends, and you can even move your friends around on the map for them if you know their whereabouts. This is another great feature that Stalqer hopes will keep people coming back to the app, or that will encourage new users to sign up.