The basic idea is similar to that of the Apple app store. The exchange is open to any software developer, from giant automakers to startups.
Once registered with the exchange, a developer can build a software solution for dealerships, perhaps with advice from others on the exchange's forums. That solution will be vetted to prove, for example, that it is secure, through a four-step review and testing process. Once it passes, the developer can sell that solution to any dealership via the exchange.
Dealerships thus will be able to choose from the offerings on the exchange any combination of, say, customer relationship management, service-scheduling and online payment software that they like, upgrading or changing providers when they wish with minimum fuss and integration time.