I use flexcar and I love it.
Whenever I want a car, I just call or go online and book a car near me to use for the number of hours I would like to use it.
It is a whole lot cheaper than owning another car, as you do not pay for gas, insurance, or maintenance. The cars are all new and clean.
You just pick one up at the place where you reserved it and then leave it at the same place.
When I am out and realize that I will not get it back by the appointed time, I just call and extend the time. As long as no one else has reserved that time, you can extend it. So far, I have been able to extend the time every time.