Carsharing is a great way of sharing. Many cars are only used by one person at the time and carpool systems, or even plain old hitchhiking, provides for more efficient use of energy and resources. In 2010 there were almost 1000 cities with car-sharing services 
Models for Car-sharing
Associations for car-sharing
Currently most car-sharing services are offered by privately owned corporations. Instead these services could also be set up as a service for and by the owners, as in a cooperative. Everyone who would take part in this scheme would be a stakeholder.
Future of Car-sharing
Electrical cars are increasingly introduced in cities. Given current technological developments it is propable that soon most cars will be based on electrical power.
This is a sharing-opportunity. Why would someone still want to own their own car when cars could be available everywhere, on every street-corner. This would also be a good way to get rid of the amounts of cars in cities.
With more sharing, privately owned cars could become unneccesary and cars could also be used as public transport.