Three simple rules govern your life.

1. Share and share alike.
2. Leave things the way you found them.
3. Springtime is best enjoyed zipping around in a convertible.

And sometimes, these rules all come together in one life-altering convergence.

Say hello to RelayRides, the new car-sharing service in town that is essentially Zipcar meets Craigslist, available now in the city.

Like Craigslist, this is a peer-to-peer operation: you rent directly from private car owners. All these generous folks are looking for is a few upstanding citizens who may need, say, something topless for an afternoon and are willing to pay big for it (or at least $6 an hour).

After signing up, you’ll go online to search for what suits your idea of pure driving excitement at the moment. For something cute, petite and European, there’s a Smart car. For something that likes it a little rough, there’s a Jeep. Arrange a pickup time and RelayRides will handle the technical stuff like insurance and how to access the car.

Of course, this situation goes both ways. If you’re willing to let someone spend a couple of hours running his hands along your rich Corinthian leather, go ahead—put your ride up on the site.

Charge more if they actually take it out of the garage.