Mirror, Mirror on the iPhone, for Free

Inner Four Inc., a Tampa, Fla., company that has 150 programs in Apple's App Store, usually devotes a couple of months to create a major app. But its biggest success so far has been one that one engineer spent just one hour on.

The ad-supported free app, called Mirror Free, is essentially a black empty screen framed by a picture frame. If a user peers closely into it, the reflection off the screen can create an effect like a mirror. By Inner Four co-founder John Swartz's own admission the app “doesn't do anything.” But the app has been a breakaway hit, dominating the top spot in the App Store's free app rankings for the better part of last week.

Mirror Free isn't the first joke app to become popular on the App Store. In the past, apps like iBeer, in which users can brew and drink a virtual glass of beer, and iFart, which does what one might expect, have taken the spotlight.