The app is based on Google Maps and works everywhere those individual services operate. When you visit Checkin Mania's website, you're presented with a map. Type in an address or a city and you'll see the checkin locations from each of the location-based networks. Clicking on a venue gives a checkin count and lists the users who've checked in. The listings usually link to more information about the location from the users of each service.
It's a basic app right now, but it's helpful -- it can be used to help you find new venues or to draw insightful comparisons between services. You can see how many checkins a location gets on Foursquare versus Gowalla, for example.
Unfortunately the Brightkite and Yelp tab selections are greyed out (the developer blames Brightkite's check-in API and Yelp's lack of one), but the app will obviously become much more interesting if and when they're activated. The app was developed by Init Labs, and it has a Twitter account that you can follow, though at present you'd be among the first.
[via Fast Company]