List of online ad servers. An ad server is a tool for placing advertisements on web sites. Typically, companies providing ad servers also provide some kind of software, interface or content management system allowing advertisers to select the ads they would like, track which ads are being served where and when, and then monitor progress over the course of an ad campaign. Other features and services may include: uploading rich media advertisements, trafficking ads based on pre-selected arameters, tuning and optimizing ads for better results, targeting ads to users by demographic or geography, and reporting impressions, clicks, post-click and post-impression activities. Some of the ad servers featured on this list include Google's DoubleClick, OpenX and AdTech.