A car share program is similar to renting a car, with the exception that you can rent the car for a few hours if you want, and the gas and insurance are included in the rental fees. It differs from traditional car rental services in the sense that it is completely self-service and is not limited by the business hours of the rental organization. There are over 1,000 car share programs throughout the United States as of the time of this writing. For more information on car share, check out: ZipCar.
Car share programs are very helpful to those who do not have a car of their own, or those who want to save on the costs of owning a vehicle. Because cars can be rented by the hour, people have the freedom to grab a vehicle for their day-to-day errands and no longer have to hassle with the schedules of public transportation. Those who choose car share programs over car ownership will save money because they are only paying for their use of the car, and don't have to worry about gas, insurance, and repair on top of any car payments they may have.
People can use a car share to car pool as they can with any other vehicle, thereby reducing the cost even further, and reducing the amount of greenhouse gases emitted into the atmosphere as they ride together instead of in separate vehicles.
As of right now, car shares are easily found in larger cities all over the world. If you are interested in finding a local car share to help you reduce the costs of owning a vehicle or as an alternative to car ownership, CarShare.net has an excellent list of cities and companies where car share services are available.