I've been working on App Map for the better part of a year, and it's really awesome to see it finally release on the App Store after a challenging approval with Apple.
The app itself lets you see what other apps are being used nearby, and what's most popular worldwide, too.

The difference between this and the App Store's charts is that people often download apps and don't use them, but this tracks this activity anonymously between users, and helps identify which apps are running on devices across a wider spectrum.
The app is free, and we'll have an update out soon to support the iPhone 5's taller 4-inch screen… I promise!

From the website:
Ride the subway, walk the dog, or fly somewhere new! App Map shows up to 8 hours of location-based popular app activity, allowing you to discover and download the most useful apps… wherever life takes you.
Find out what is actually being used worldwide, and not just downloaded!
… Hope you like it! It'll be an interesting platform to work on, for sure. — Expect a lot from this idea. 👍🏻