谷歌和AppNexus都一头扎进了这一领域，但两者的道路自然不太一样。奥凯利回忆称，他最早为AppNexus寻找投资者时，大部分硅谷风投公司还不怎么愿意投资总部位于纽约的初创企业——虽然AppNexus后来得到了“超级天使投资人”罗恩•康威、风险投资公司Venrock和First Round Capital以及其他方面的支持。相比之下，谷歌则拥有足够的内部资源来打造这块新业务，它凭借自身在互联网领域的广泛涉足和一些大刀阔斧的收购（从2007年收购网络广告服务商DoubleClick到去年收购在线广告平台Admeld），已在实时竞价领域实现了迅速扩张。
When you visit just about any website these days, ads appear as the site loads. But what you can't see is that many of those ads were not predestined for your eyes -- advertisers won the spots in near-instantaneous auctions occurring in the quarter of a second between click and use of the site.
Real-time online advertising through such auctions is a rapidly growing business, and Google (GOOG) has made it a critical part of its advertising ecosystem. But the far smaller AppNexus has emerged as another leader by taking a page out of Google's playbook.
AppNexus is a product of CEO and co-founder Brian O'Kelley's goal of broadening the online ad exchange platform that he developed with Right Media (which he sold to Yahoo (YHOO) in 2007) to offer an open market that works across the gamut of software platforms that companies use to buy and sell online ads.
The ad exchange itself emerged to solve one of the major problems of online ad sales: much ad inventory (spaces where ads appear online) would go unsold as buyers and sellers couldn't always match up in time. The first step was for companies to aggregate their available ad across a swath of sites, says eMarketer analyst Lauren Fisher. From there, basic exchanges emerged, increasing the scale of ad sales, and real-time exchanges have become the latest turn of the wheel.
Google and AppNexus both plunged into that space but, unsurprisingly, their paths have not been so similar. O'Kelley recalls that when he was first seeking investors for AppNexus, Silicon Valley venture capital was largely steering clear of New York-based startups -- although the company would receive backing from "super angel" Ron Conway, Venrock, First Round Capital, and others. Google, on the other hand, had the resources to build from within, and has grown rapidly in the advertising space thanks to its extensive reach on the web and some aggressive acquisitions, from DoubleClick in 2007 to Admeld last year.
But ask members of the ad tech space about real-time ad exchanges, and you'll probably hear both companies mentioned in the same breath. For Google, the exchange is "one key piece of the puzzle" in producing an end-to-end advertising solution, according to Neal Mohan, vice president of display advertising. Google's exchange has grown 150% in the last year, Mohan says, with much of the sales from within its own network and clients of other ad managers like DoubleClick.
In online display ads, Google is everywhere -- and many small companies that compete with the search giant in one cross-section of the online ad world are themselves Google customers. Google's goal, Mohan says, is to cut out the friction between different ad technologies, making the process easier for everyone, even those sometime-competitors.
One company that is taking advantage of Google's "open" approach is MediaMath, which offers a platform catered to marketers who want to buy ad space, using several suppliers including Google and AppNexus. MediaMath CEO Joe Zawadzki says that AppNexus might be beating Google at its own open-platform game.