In 2006 when I first got into affiliate marketing I realized that all of AdSense income was coming from people advertising affiliate offers. Now even though I was doing affiliate offers of my own on the site I wanted to try going direct.
So we built our own internal system that made some AdSense Looking ads but allowed us to put our own copy inside.
My CPC immediately went up 3x.
Then we decided to make this so anyone could use it. I was killing it at the time so I was like lets just do it for free. It was a week project for us and it was up and running.
We called it ShoemoneyAds (what else).
Check the walk through video here:
I am sure some of you reading were using it ;).
This eventually became AuctionAds, a company that grew rapidly in users and revenue until it was sold in 2007.