What the Magic Muggle Clock does do is show you where your foursquare friends are based on the type of place of their most recent check-in.
If you’re not necessarily interested in knowing the exact location of all of your friends, the Muggle Clock displays check-ins by category, so you’ll be able to see how many of your friends are currently a store or eating at a restaurant.
It’s a fun visualization for foursquare that takes the data available on its API and displays it in a quicker and consumable way as opposed to the actual foursquare app.
Simply log into the app with your foursquare account, and Magic Muggle Clock will display a snapshot of what your friends are up to. It’s one of those “second monitor” visualizations like Arrivals and 4SQoogle, that makes interacting with foursquare on your desktop a source of entertainment.
The app updates in real-time, and it’s fun to watch the hands of the clock swing as your friends move from place to place with their check-ins.