Before anyone knew what location aware apps were, before Foursquare, MyTown, and the like were house brands, there was Loopt. Everyone on the planet (maybe a slight exaggeration) had Loopt, but nobody really knew what to do with it. After a few weeks of use, Loopt eventually became a personal stalking app for the willing, allowing you to knowingly let your friends GPS track you as you go about your day. Years later, Loopt has hit 4.0 and is still trying to show its 4+ million users why it is relevant. Now though, it really is pretty neat.
Like before, Loopt works by connecting you to your Loopt friends (who I'd hope are your real friends) by showing you where everyone is on a map. Instead of just tracking people, Loopt is now socially aware, allowing you to not only check in to places, but also invite friends to where you are at. Let's say that you go to your favorite burger place and want your friend(s) to join. Instead of leaving the app to send some texts, Loopt allows you to punch in a message (called a Ping) that instantly alerts the other users mobile device (allowing them to send a "Pong" with their location and reply).
Working nice with Facebook Places, Loopt is now a fully operational check-in service too. You can't become the mayor of every place you walk to, but it does have a really cool area that shows you what is going on around town and which places your friends like the best. With the location aware feature, Loopt also tells you when and where rewards are around you that companies may have left for people checking into certain places, just to add something tangible to your check-in experience.
Also nice, and of interest, is the ability to toggle and edit the auto update feature. Instead of just blasting out your location for everyone you know to see, you can choose who sees you and where. If you want everyone still tracking you, you can do that, but if you want certain people to only see you if they are within a certain range, or not at all, you can do that too.
As always, Loopt is a completely free app and can be downloaded right now in the App Store. Getting users to download it years after it was all the rage could be an issue, but the new features just may make it worthy of a second (or third, or fourth) look.