You may have seen Clearwire's Got Clear? app back when it was released in mid-August, but unless you subscribe to Clear service, you probably didn't think it had anything to do with your HTC EVO 4G. Based on how many times the app has been downloaded in the past two months (less than 10,000 according to stats from Market), you weren't alone.
Even though the Clear and Sprint 4G services are marketed individually, they are both using the same network: Clearwire's network. The company currently operates the only 4G network in the US and markets the service through its own brand (Clear) and through partnerships with Sprint, Time Warner Cable, and Comcast. In other words, the Got Clear? app is something that can be quite useful for EVO owners.
Using Google Maps (viewable in satellite, map, and hybrid modes), the app identifies your location and shows you both indoor and outdoor 4G coverage. You can zoom in/out by double-tapping or using the on-screen controls, move the map around (rendering can be slow here), and search for other locations to see if they're 4G areas, which is really useful when traveling.
It may not be an app you use often, but it's free and only takes up 340KB of space on its own. Accessing the maps fills up the cache and data pretty quickly, though, so you should probably clear those every now and then.