My father told me never to get into a car with a stranger.

I wonder how he’d feel about it if an app existed that knew which strangers were trustworthy, and which were, perhaps, even potential friends? And what if this app could also arrange for me (when I’m carless and in a rush) to get convenient lifts from these new friends?

As of November 2, Seattle has just such an app thanks to San Francisco-based SideCar, a ride-share service that grew quickly enough—50,000 rides so far—to inspire CEO Sunil Paul to expand it in Seattle.

The service establishes a peer-to-peer network of drivers and riders that runs on per-ride suggested donations rather than fees; and it emphasizes the social fun of making new friends and connections.

Paul chose the name “SideCar” to conjure a sense of playful adventure (think: a superhero’s sidekick clad in scarf and goggles). Paul claims that users soon come to see it as their “secret transportation advantage.”

Creating an account takes about 30 seconds, and a handy feature will even scan your credit card for you. Then, using Google maps, you simply position a map point at your pick up location and another one at your drop off location. You can select a particular driver or simply opt for the closest driver and then select “Confirm Ride.” The name, picture, vehicle details of the driver and ETA appear on your screen, and you can push a button to call the driver.

When the ride is complete, you have the option to rate the driver and choose a donation amount (the field is pre-populated with the current average donation).

Okay, but what about that risky bit where you’re getting in the car with a stranger?

SideCar addresses safety issues by pre-screening driving and criminal records of those who wish to volunteer as drivers. Additionally, the rating system allows both drivers and riders to review each other. Riders can also share a real-time map with a friend.

I tried SideCar last Saturday night. After confirming the ride, my driver, Camille, picked me up outside my neighborhood Safeway just two minutes later in her black Jetta. She was a safe driver and a friendly person, and the suggested donation was less than cab fare would have been. As SideCar claims, the experience was much closer to getting a lift from a friend than it is to a cab ride.

To give SideCar a spin, download the SideCar app for iPhone or Android and follow the instructions to set up your account. For now, SideCar is available in Seattle on Friday and Saturday nights from 6pm-2am.