They actually do rent manual cars: I searched a random day in April and 3 of the 10 cars available are manuals (https://flightcar.com/cars/SFO/2013-04-02%2012:00:00/2013-04...). This seems like a great benefit if you're looking to rent a manual car, since car-rental places don't usually offer them.
That's very cool. I wouldn't rent my manual though, heh.