Founded: 1998

Sergey Brin and Larry Page are the latest billionaires to get their start in a garage. But while Bill Hewlett and David Packard and Steve Jobs and Steve Wozniak worked on wood benches and dealt with cold drafts, Brin and Page enjoyed relaxing breaks in the backyard hot tub. The pair, who rented the garage from a woman who’s now Brin’s sister-in-law, bought the house last October to preserve this piece of the Google legacy.

Founded 2004

Co-founder Mark Zuckerberg started the company at Harvard’s Kirkland House dorm, in the suite he shared with roommates Dustin Moskovitz (now VP for product engineering) and Chris Hughes (once a company spokesman). Facebook’s success is already legendary, although Zuckerberg now faces a federal lawsuit alleging that he stole the idea from a rival social-networking site.

Founded: 1995

Newmark’s classified-ad site grew from humble origins: a list of notable upcoming events that he e-mailed sporadically to Bay Area friends. He worked out of this two-bedroom apartment on Cole Street for six years; he moved the company to nearby offices in 2000 but lived here until he sold the apartment in December 2005. Now 17 million people visit Craigslist each month.

Founded 2002

In an ordinary office cubicle, intern Blake Ross and programmer David Hyatt were working on a new browser for Netscape’s Mozilla project after Netscape Navigator was crushed by Microsoft’s Internet Explorer. The browser was called Firefox, and it became the first to give Explorer real competition since Navigator’s market share collapsed. Both men left Netscape before it was disbanded in 2003, but the Mozilla project lives on.

Founded: 1999

Second Life was born on narrow Linden Alley in San Francisco’s quaint Hayes Valley neighborhood. Founder Philip Rosedale worked in the warehouse with a single engineer. Three years later he moved to a larger office on, naturally, Second Street. Company headquarters are now in San Francisco’s financial district, while the original space on Linden is occupied by a Moroccan furniture store.

Founded: 2004

Kevin Rose was hosting The Screen Savers on now-defunct cable channel TechTV when he interviewed Apple co-founder Wozniak, whose tales of Apple’s early days inspired Rose. Later that day he went back to his apartment and hatched an idea for a news site that would let users decide what went on the front page. More than 17 million people get their news through Digg every month.