General Motors has formed a brand called “Maven” that will run its car-sharing ventures, including a new one that will begin competing with ZipCar next month in Ann Arbor. GM executives see big changes coming with ride-and-car-sharing. Maven already has 21 parking spaces and new GM vehicles assigned to the area around the University of Michigan campus in Ann Arbor, including dormitory lots. It’s also expanding a residential car-sharing project to more apartment buildings in New York City and to Chicago.