Most of the applications on Apple's iOS App Store are un-downloaded, unranked, and largely invisible software options.

These applications, estimated to account for around 400,000 on the App Store, have been dubbed "zombie" apps by new mobile analytics and ad firm Adeven and its Apptrace tool. Company CEO Christian Henschel said in an interview with Gigaom that he believes it's "really tough" for smaller, independent application developers to be discovered in the current App Store structure.

"The reality is there are only a couple of thousand apps that really make some kind of downloads," Henschel said. "This is based on Apple's closed system â it's tough to discover those kinds of apps. You don't have proper search, so the only way to discover new apps is through the top listing."

Apple announced in June that downloads on its iOS App Store had reached 30 billion total, while $5 billion had been paid out to developers. There are more than 650,000 applications available on the App STore, with 225,000 of those built specifically for the iPad.

Apple has continually worked behind the scenes to improve discovery of content on the App Store. Last month, some developers reported that Apple had tweaked its search algorithm to favor topically relevant results and applications that receive more downloads, though the changes were quickly reverted.

Earlier this year, Apple acquired Chomp, a mobile application search engine for a reported $50 million. It's expected that the acquisition is intended to enhance software discovery on the App Store.