Room to Rent, via the Web

When Lisa Marion’s roommates moved out of her apartment in Toronto in February, she scrambled to find replacements. But instead of finding one or two, she found 30.

Ms. Marion, 26, has been using Airbnb, a Web site that streamlines the process of renting out her extra bedrooms to travelers. The service has unexpectedly turned her into a bed-and-breakfast owner, bringing in roughly $1,800 a month, a nice cushion as she works on starting her own business.

“It pays my rent with a little left over,” she said. “I’ve been able to upgrade my place, paint and get new furniture, which in turn means I can charge more.”

Airbnb, which says it is handling 10,000 guests a night, is at the center of a boom in new companies that are creating a market for places to stay — a spare room, a house when the owners are on vacation or even a backyard treehouse.

Some of these businesses are riding the surge of interest in all kinds of Web ventures; Airbnb plans to announce on Monday that it has raised $112 million from investors. Last month, Wimdu, a similar venture in Europe, raised $90 million. Smaller competitors like 9flats, Roomarama and iStopOver are also hoping to take a bite of the short-term rental market.

These companies say they are helping hosts like Ms. Marion become microentrepreneurs, while giving adventurous travelers insights into how local residents live, whether they are visiting Japan or Los Angeles.