In Chicago there are two "quick car rental" options (that I am aware of) - Zipcar and I-Go. Zipcar is a for-profit company, and I-Go is a non-profit organization. A long time ago when we first started this blog I-Go sent me an email asking to mention their cars on the blog but I had no idea who they were and assumed it was spam...
Zipcar seems to have a lot of cool cars, such as Honda Elements and even BMW's and Volvos. A friend of mine joined recently so we picked out a Mini Cooper and made a reservation (you need to pay to join Zipcar).
Renting these types of cars is fundamentally different than the "traditional" car rental. These cars are scattered throughout the city, in ones or twos, in parking lots . They are identified by the Zipcar signs like the one above by the car we rented. Instead of renting the car by the day and then paying a whole bunch of extra charges like insurance, mileage, etc... the Zipcar rents by the hour and you only pay for the hours that you use. Gas is included, with a fleet gas card (we didn't use it, so I don't know exactly how they avoid fraud) under the visor.
You order online, through a web site. You have a car and then your card allows you to unlock the car, and the keys are in the car already. Here you can see the key card, the transponder-type thing in the upper left above the steering wheel, and the key holder that holds the ignition key on a string near the starter.
Our car was named "Mystique" and it was a red Mini Cooper. We rented the car for 2 1/2 hours which included insurance and gas for $28. As I noted above we didn't have to refill the tank because we only drove a few miles but it was included in the price.
The tag line for Zipcar is "wheels when you want them" which was true, since the car was ready and waiting as promised. I guess you could be SOL if you pick a time to rent and the previous driver doesn't show up because your rental is for a specific car; you can't just pull a different car off the lot like you can for Hertz (although you probably could call Zipcar and if there is a different car in an adjacent spot maybe they could rent you that one, instead).
The Mini Cooper was surprisingly big in the back seat and the interior had a lot of interesting touches. The car was very slow, however, which probably wasn't helped by the fact that it carried 4 adults (we did look like we were getting out of a clown car). The car was also FILTHY; this is one drawback when compared against Hertz because they always wash and vacuum the car before people take it off the lot. My friend who rented it called Zipcar to tell them to wash it when he was done and they sent him a thank you email.
All in all it was a good experience. If you live in the city and don't want to pay for parking, insurance and a big car payment this might be an option. In general it isn't good for all day rentals because it is not economical against "traditional" car rental companies but for 2-3 hour trips it is perfect.
Zipcar really seems to have solid technology. It is amazing that the key card works to unlock and run the car and you can do everything on the web. It seems more efficient than the traditional car rental process, as far as people. Of course, it would have been nice to get into a clean car, too.
I haven't tried I-Go and can't comment on them but both of these options seem to be good ideas for people who need a car occasionally but don't want to rent for the entire weekend. The check in and check out process was also much quicker than the traditional car rental companies, and we didn't need to go to an airport to get it done.