There are two trends that have been dominating the App Store since its earliest days. One, free iPhone applications that mimic a simple real world device in a minor way and two, applications that put the word FREE into their name so as to remind people that it is a free iPhone application. Few of these qualities ever lead to a great free iPhone application, but they still get a high level of popularity.
Air Horn (FREE!) for the iPhone is one of the newest in this string of cheap iPhone applications. Air Horn (FREE!) simply mimics what an air horn does, which is to make a loud sound. Yes, Air Horn (FREE!) will make a loud sound. Mystery solved. Along with the image of an air horn that you press to make the sound are banner ads, which are always fun.
There is little reason to download Air Horn (FREE!), but if you really need to turn your iPhone into an annoying reminder that the App Store is not always at the top of its game then you are ready to go.