OpenAds - now OpenX - was this tool for a very long time.
There are a couple of drawbacks. First, it turns out that there's not much money to be made developing that software. Second, it turns out that running it is a lot of work, to the point that it's not worth it for most people. Third, most ad buyers don't want to juggle dozens of small publishers, they want centralization.
There are a couple of drawbacks. First, it turns out that there's not much money to be made developing that software. Second, it turns out that running it is a lot of work, to the point that it's not worth it for most people. Third, most ad buyers don't want to juggle dozens of small publishers, they want centralization.