#6: Cooliris, 28.5 million+ mobile visitors per month
I have to admit, I didn’t even know what Cooliris was before I made this list. Previously known as PicLens, the company makes slideshow software as well as plug-ins that allow you to review thumbnail pictures, web pages and other content on your mobile device before you click through. Not flashy, but certainly one of those pieces of software that many people use without even knowing it. Cooliris also has a number of fancy iPad apps like Discover, Liveshare and Decks. The company is very much in the startup phase, and is based in Palo Alto, Calif.