What's the best free ad server? I've looked into OpenX OnRamp. I want something simple. I am only dealing with 3 ad networks and 2 of them don't fill more than 50%, so I want to be able to show 1 of the ad networks 50% of the time it fills and then back it up with the other ad network the rest of the time. I can't do it by backing up with 1 ad network when the other isn't filling because they don't cooperate correctly.