The plan has been for Google to become the full-service advertising platform supplier on the Internet, and DoubleClick is a big piece of that puzzle. But the company's big goals have always started small, and today's new beta is just one more example.

Throughout its short history, Google's approach to the software side of its business has been to let the code fly free, and monetize that investment through the sale of services to the segment of the market that can afford them. With its DoubleClick acquisition now complete, that approach changes a bit, since that firm's DART tools for publishers represent a lucrative revenue source in both the code and services department.

But the picture of Google's post-acquisition strategy became a lot clearer this morning, as DART is being positioned as a toolset for major online publishers to manage their advertising inventory across multiple brands and sites. At the opposite end of the spectrum comes Google Ad Manager, which will be marketed similarly to Google Analytics as a free tool with a modicum of free service for small online publishers to make sense of their advertising sales strategies.

Of course, the software is geared toward making it easier to fill inventory using Google's services. For example, you use it to create ad slots that have premium and moderate price points. Placements group one or more slots into sellable quantities (for instance, the leaderboard along the top plus the skyscraper along the right), and ad products represent your customer's view of how you sell space on your site -- which placements, for how long, at what cost.

But all this is geared toward using Google as the underlying platform. As one way of maximizing that feature, unsold inventory can be filled using AdSense, where Google chooses which of its clients fill your space based on context.

As senior product manager Rohit Dhawan wrote this morning, "Some publishers use ad networks like Google AdSense to fill their ad space. Still others employ a direct sales force to manage and sell their ad inventory with solutions like the DoubleClick Revenue Center, and partner with third-party ad networks to fill in any unsold space. Regardless, it is a challenge for publishers to effectively manage their available inventory and ensure all of their clients' campaigns serve on time without a sophisticated ad management and ad serving solution."

That's where Ad Manager fits into the picture, as that certain something in-between. And Google has seen success with this strategy before with its Analytics package, addressing small businesses with tools they've probably never known they might need before, and supplementing those tools with services that could draw them in as customers.

The Ad Manager beta is by invitation only, and the company is taking applications now.