Lee Jae-Won/Reuters

Technology start-ups continue to chip away at the idea that everyone should own a car or two.

The latest twist on car sharing comes from a company called SideCar, which introduced its service in San Francisco on Tuesday. The service allows people seeking a ride to use a smartphone app to find someone willing to give them one in their own car. When it works well, it takes about the same amount of time it takes to catch a cab. The company has been in a private testing period for several months and claims to have hundreds of drivers and thousands of riders already using the service. It has given 10,000 rides in total. The company has attracted investment from several venture capital firms and angel investors, as well as Mark Pincus, the co-founder of Zynga.

There have been car-sharing services available for some time, from the now-ubiquitous Zipcar to peer-to-peer services like Relayrides and Getaround. The idea of using a smartphone app to catch rides with limousine drivers between assignments also caught on last year with a company called Uber, which also started in San Francisco.

Of course, Uber is essentially just an expensive black car service with a novel way to call for a ride. The idea of ride sharing, which would leverage smartphones to save people money while offering a taxi-like service, is potentially more disruptive because it cuts out professional drivers altogether. It has been a tough nut to crack, however. Several attempts to allow ride sharing in New York City taxis, for instance, have fallen flat.

SideCar’s pricing is set up to be rider-friendly. The app tells riders how much others have paid for similar rides, but leaves it to them to decide how much to pay. The main deterrent to being a cheapskate is that doing so will hurt your standing within the community. Riders and drivers rate one another at the end of each trip, so freeloaders may soon find it hard to find chauffeurs for future rides.

Matt Johanek says he has been giving between five and 20 rides a week since April. Every single rider has paid at least the suggested fare, he said. Mr. Johanek occasionally sets aside time to shuttle strangers around town, and ends up earning enough to pay for his gas and insurance. There have been nonfinancial benefits, as well.

“I’ll admit I’ve gotten a couple of dates out of it,” he said.

Of course, not everyone looking to get across town is interested in sparking a romance, and attempting to avoid uncomfortable social situations is a fact of life for collaborative consumption companies like Airbnb, TaskRabbit and others. SideCar says it checks potential drivers’ criminal backgrounds, driving records and insurance.

Tech services that connect people in the physical world are inherently vulnerable to losing the trust of their users because of abuses by a few users. But even without anything bad happening, some people are simply more comfortable with some kinds of interactions than others.

Cynthia Yeung, who has been using SideCar regularly, said she trusted its internal rating service, and had never balked at taking a ride from a stranger. At the same time, she cannot bring herself to rent a room through Airbnb.

“Sitting in someone’s car is a little different from sleeping in someone’s bed,” she said.

Another question is whether insurance companies will balk if their customers begin using a service like SideCar to turn their private automobile into a business. Sunil Paul, SideCar’s chief executive, helped pass share-friendly legislation in California. (He has also been flirting with various car-sharing business ventures since the 1990s). He said that the current standard for what people can do with their private vehicles will easily cover the type of mini-businesses that people might run through SideCar.

At the same time, Mr. Paul does anticipate potential legal complications that could come with success.

“Long term we are concerned, as are all of these share economy companies, that incumbents will use regulation to hold back innovation,” he said.