What if there was a company that had paid mobile and social app publishers more than $100 million in ad revenue and driven 200 million app downloads to date but almost no one knew about it? What if that same company was serving billions of monthly ad impressions to 300 million unique Facebook users and 160 million unique mobile users? How could a company like this stay under the radar?

Until recently, LifeStreet Media has purposefully kept behind the scenes. It’ll have a much harder time doing so after today’s announcement of its $66 million financing led by Nautic Partners. The company has not released information on any previous financings, however it is reported to have raised only $3.6 million to date.

LifeStreet delivers monetization to application developers while connecting advertisers to highly targeted audiences on mobile and social networks. The company is the leading third party-source of ad inventory for Facebook, iOS, and Android app developers.

It also specializes in user acquisition and counts as its advertisers many of the same developers into whose apps it serves the ads. This incestuous cycle is part of the genius behind its business model. LifeStreet’s website includes the cliché promise, “You make the app. We make it famous.”

The company’s in-app monetization engine, called RevJet, incorporates proprietary and patent pending “Universal Object Serving” technology which optimizes ads based on customizable metrics established by its app publishers and advertisers. The software applies what LifeStreet calls “iterative high velocity testing” to up to 10 thousand combinations of ad components per second, such as background color, copy, headline, and placement. The end result is meant to be the right ad for the right audience at the right moment.

Its customers prioritize various metrics such cost per install (CPI), cost per acquisition (CPA), cost per post conversion event (CPX), or cost per click (CPC). LifeStreet then optimizes the ads delivered based on the desired metrics. Since the company charges solely based on performance, its customers pre-determine how much they want to spend to achieve a desired event and only get charged if LifeStreet delivers at or below that price.

Mitchell Weisman founder and CEO of LifeStreet told PandoDaily:

With LifeStreet, testing is no longer episodic. We test any and all revenue drivers impacting ad performance perpetually at incredibly high speed and with multiple variables simultaneously. We combine visual elements (copy, background color, or placement) with logical (algorithms). We can tell you whether your buttons should say “click here,” “click now,” or simply “click,” which campaign to select based on demographics, and what data horizons to focus on based on targeted outcomes. We deliver the highest CPMs anywhere. North of two thirds of all social and mobile developers have worked with LifeStreet as a publisher or advertiser.

Keeping to its theme of discretion (or stealth), LifeStreet rarely discusses specific clients. The only one mentioned by name during our interview was Zynga, although the company’s website includes the logos of Crowdstar, Zoosk, and others as well.

Within six months of entering the Facebook ad marketplace in 2009, LifeStreet passed Google AdSense to become the #1 third-party ad supplier. It also out-competed social advertisers Adknowledge and RockYou, which have themselves each raised hundreds of millions of dollars previously. In mobile its principal competitors are Greystripe and Millenial Media. LifeStreet claims that publishers earn more with its services than anyone else in more than 85% of test cases.

LifeStreet was named Inc. Magazine’s 362nd fastest growing company in 2010, with revenues of $40.7 million at the time and 816 percent growth over the previous three years.

Weisman says, “We have resisted raising money for a long time. We’ve had many choices including larger offers at higher valuations. We chose to raise capital now to continue our growth as well as to provide liquidity for early investors and founders.”