OpenX has an open source offering which has a plugin framework for adding your own functionality to it. Building an ad server that'll meet the needs of larger

OpenX has an open source offering which has a plugin framework for adding your own functionality to it. Building an ad server that'll meet the needs of larger online advertisers can be a real pain, especially if it's just a single component of your business. If I were you, I'd see if I couldn't just extend the open source version of OpenX with a custom plugin. If it turns out that you can't, well -- you can still learn a lot about ad servers by playing about with OpenX's code.