Welcome to WebmasterWorld Guest from 188.8.131.52
This is the one that's included with Cpanel/Fantastico - free.
I tried this on a niche, locality based site, with only partial success. It was supposed to be a totally focused on the site's topic and locality but I was forever deleting off topic and out of area ads (usually both). In the end it was too much work and never achieved a critical mass to be a useful service so I dropped it.