List of ad exchanges online. An ad exchange is a platform or system allowing advertisers and publishers to buy and sell online advertising inventory across a variety of ad networks. In other words, is a marketplace for online advertising, usually operating in an auction-style system of "bids" for ad space. It is an attempt to make online media and advertising sales a more structured and open process, eliminating the use of ad networks as middle men and increasing the efficiency of individual advertising deals. Some of teh exchanges incldued on this list are DoubleClick, AdECN and OpenX.What are the top online ad exchanges? Take a look at this list and you'll learn about the top online ad exchanges.