Since its launch in 2007, Apple's (NASDAQ:AAPL) iPhone has attracted a devoted following. It has also unleashed a booming aftermarket of companies creating games and tools for the iPhone-wielding masses. This year, Apple rolled out a kit for developers interested in creating iPhone-specific software, as well as the App Store, an iTunes offshoot, at which they can sell their products. The store has an inventory of more than 3,000 applications and has processed 100 million app downloads. Here's a look at some promising players.

FileMagnet, a tool developed by Magnetism Studios in New York City, lets users wirelessly transfer documents and files between a laptop and an iPhone. FileMagnet is $5 at the App Store, and The Wall Street Journal's tech guru, Walter Mossberg, included it on his list of apps that are worth checking out.
Number Of Downloads: 100,000

Before Apple opened up the iPhone to developers, Andrew Lacy, founder of Tapulous, bought the rights to a game that was popular in the world of illicit apps. His Palo Alto, California, company spruced up the game, renamed it Tap Tap Revenge, and then legally launched it when the App Store opened. Now it's a hit. Number Of Downloads: 2.15 million

Tap tap tap, a Littleton, New Hampshire, company, developed an app called Where To?, which uses an iPhone's built-in GPS to direct people to nearby points of interest. Developer John Casasanta is a marketing dynamo: He helped launch, a marketing site run by a group of longtime Mac developers, and his outspoken blog draws 100,000 visitors a month.
Number Of Downloads: 50,000

San Francisco -- based Ngmoco marries social networking and gaming. The company's software lets players see other players around them and compare scores. Ngmoco works with indie game developers, who embed that software into their iPhone games and publish them on Ngmoco's platform. Number Of Downloads: None; Ngmoco's tools will be embedded in 13 new apps.

The Line: With more than two million downloads, Tapulous has a great head start. Thanks to its relationships with multiple developers, however, Ngmoco could prove to be a closer as the market matures. "Instead of trying to build a bunch of little hits, they are trying to build gaming into a social platform," says Matt Murphy of Kleiner Perkins's $100 million iFund, which has invested in the company.