So, what is essentially ad aggregation network you might wonder. You certainly know ad network businesses. Even if you think you don't, you encounter them everyday. One of the largest ad networks is the Google Adsense. Another example of huge ad network is DoubleClick, well, Google owns this one as well.
Publishers can sign up with an advertising network, place a snippet of code on their website, ad supported desktop application, or recently added mobile applications on iPhone, Android and Blackberry. Once the appropriate code snippet has been placed, the ads will start to flow to your visitors/users. You don't have to worry virtually about anything except how to drive more traffic to you website/application and optimize the ads to give you best revenue. And that in fact makes a lot of sense to the publishers, since worrying about those two is quite enough to begin with and should be the only concern of the developer and/or publisher. Using advertising network relieves you from worries about where to get advertisers, how to bill them, implement an advertising platform so that you can track what is going on with the ads etc... etc...
Let's take a glimpse into the history of online advertising. (All said, also applies to software advertising as well, but online advertising accounts for such a large portion of the "computerized" advertising, that I will just mention "online" advertising).
Since the appearance of online advertising, certain companies understood that being the mediators between the publishers and advertisers is very solid and profitable business model and many companies made big utilizing this business model and still continue to make great profit out of this business.
Those advertising platform companies did not appear right away. There was a considerable amount of time when advertisers and publishers will "manually" find one another and negotiate rates. The usual business incentive quite unsurprising applied here as well. If you were a small publisher, it was up to you to try and find advertisers to sustain you online business model. However if you were reasonably large publisher, advertisers will line up for available space on your website.
You can imagine what a pain it can be to find an advertiser if you are a small web publisher. You would have to spend considerable amount of time solving this problem, instead of worying about improving your publishing media. This deficit was identified when the problem become large enough to be noticeable and to be profitable. Companies started to aggregate advertisers and publishers and act as a mediator (or the middle man) usually in highly transparent manner for both advertisers and publishers.
When you concentrate on doing one thing, you would usually do it much better than if you would be concentrating on doing several things. Since those mediator businesses were concerned just about one task, they could offer much reacher experience both to publishers and advertisers, suplying advanced management and statistics tools. Advertisers were getting tools to make their campaigns target more specific audience and publishers in turn could receive much better revenue for the traffic.
Now we getting to the present where online advertising seems to be outgrowing the current model and requiring additional layer of aggregation. That's where the ad aggregation and mediation networks come into play. Those networks do what ad networks did in the past. They aggregate advertisers and publishers, but instead of direct aggregatio, those mediator networks aggregate another ad networks. Those are essentially meta ad networks.
It would be interesting to see how successful those meta networks will become with time. Right now it is too soon to tell.