We just installed OpenX's free software onto our servers, with some pain, but now it runs wonderfully. (Our needs are very specific, but not complex.)
After we got it installed, we were approved for OpenX's free hosted ad server biz. We had tried the free Google Ad Manager and liked it OK, but it was weak on Geo location via IP, which was important for this project...
But, in the meantime, I got familiar with Google Ad Manager's biz model, which neat: You sell ads on your site and Google will fill in with what you can't sell. That thinking work fine for us. We are, of course, using Google Ads with OpenX now in some slots.
All of that is to say, Open X has been planning to start OpenX Market, saying they are planning to go Google Ad Manager one better. From what I can tell, it is something like a targeted affiliate program with an ad manager, of which the webmaster controls. (It's more work, but it's more money, in theory. I am still looking for less work, more money...)
But, of course, it's all in beta or alpha and such at OpenX. I happen to know that they have some people working at OpenX who have been to the dance before--some ex-Yahoo executives, for example. It's worth watching. Here is Matt Asay's recent report on Cnet: