A lot has been said about Facebook's new Places service but it's far from the first geo-location service for smartphones.
Glympse, which has been around for more than a year, offers a very different type of service. Instead of checking you into a location, it allows you to send someone a message with a URL that lets them track you via a Web page or via the Glympse app on their smartphone.
As a form of protection, any tracking session automatically expires after a certain period of time, ranging from 10 minutes to four hours, and there is no way to extend it beyond four hours without establishing another session. Glympse doesn't let you "check in" to places but it does show your location within a few hundred feet.
One fun feature is that it can track you in a moving vehicle and even display your speed. A few months ago I took the Bolt Bus from Washington to New York and displayed my location to my friends and Twitter followers as we were driving on I-95. Several people wrote in that the bus driver was exceeding the speed limit. It's a good thing for him that I apparently don't have any New Jersey State Police officers among my Twitter followers.
Although Glympse isn't marketed as a kid or spouse tracker, parents can encourage their kids to "send them a Glympse" when they're out and about. I've even used it to let my wife know I'm OK when away from home. As long as she can see an image of my car moving on a map, she knows that I'm making my way home.
In general, it's a good idea to put some thought into any location service you consider using, and it's especially important for parents to talk with their kids about the safe use of location services. ConnectSafely, the nonprofit Internet safety organization I help operate, has some tips on location sharing services that you can access here.
Disclosure: Glympse (along with geo-location competitors Loopt, Google and Facebook) provides financial support for ConnectSafely.org, a non-profit Internet safety organization where I serve as co-director.