People seeking a set of wheels traditionally had two options: buy or lease. But the advent of ride hailing turned the next generation of drivers into backseat riders. Now app-based subscriptions—think car sharing that’s paid by the month, not the hour—are vying for consumers who fall between Uber addicts and car owners. Car sharing is projected to grow globally from 5.8 million users in 2015 to 35 million by 2021, according to Boston Consulting Group.