As the World Wide Web evolves into a more collaborative platform, the technologies and business models involved in that transition are being swept up into the "Web 2.0" rubric, a term vague enough to encompass almost anything one cares to push under its banner, but catchy in summing up the widespread sense that the Internet is at a tipping point.

The idea that the Web is transitioning to a new era, however, is grounded in real examples. Beneath the hype generated by the concept is a growing number of pioneering sites that are offering new, collaborative services, underpinned by new business models.

IT publisher Tim O'Reilly, who coined the term for the debut Web 2.0 Conference in San Francisco in October 2004, was hard-pressed to define the term more concretely for the second conference. He resorted to offering a list of companies exemplifying the idea that the Web is evolving from a collection of sites controlled by individual publishers into an interactive platform.

Pioneering online advertising sales platform DoubleClick is a Web 1.0 service, according to O'Reilly. Google's open-to-all-publishers AdSense network is Web 2.0. Photo album hosting site Ofoto is Web 1.0, while the more interactive photo hosting and community site Flickr is Web 2.0. "Like many important concepts, Web 2.0 doesn't have a hard boundary, but rather, a gravitational core," O'Reilly wrote in his essay. (Which can be seen on his site: http://oreillynet.com/lpt/a/6228)

Flickr illustrates the power of the new model, industry executives say.

"They created an ecosystem and a phenomenon much larger than what you would expect a small team to be able to do," says Bradley Horowitz, the director of technology development for Yahoo.

Yahoo was so taken with Flickr that it bought Flickr's tiny parent company, Ludicorp Research & Development, last March for an undisclosed sum. It followed with a December buyout of del.icio.us, a community-focused bookmarking service that attracts the same kind of buzz Flickr earned.

The photo-sharing site launched in February 2004 and quickly built an audience attracted to its elegant interface and community features. Unlike more traditional photo-album sites, Flickr emphasizes sharing; its style incorporates hooks popularized by blogs like classification tags and reader comments. The site also demonstrates the sophisticated resources developers now have access to: A group of less than a dozen people built Flickr, which uses the open-source PHP scripting language and runs on free MySQL database software.

Yahoo's portfolio of acquired applications also includes group events calendar site Upcoming.org, music playlists swap site Webjay and blog updates tracker blo.gs.

Among media giants, Yahoo is jostling for the Web 2.0 vanguard position with its longtime search rival, Google.

Google, too, keeps an acquisitive eye on promising startups. It shook up the blogging world in 2003 by purchasing Pyra Labs, a small venture that developed the popular Blogger service, and later picked up photo software developer Picasa to jump-start its photo-sharing services. In May, Google acquired Dodgeball, a mobile social networking venture that lets cell-phone-toting users locate nearby Dodgeball-registered friends.

Dodgeball's founder, tech developer and analyst Dennis Crowley, began toying more than five years ago with ideas about connecting cell-phone users through social networking software. When he and his partner Alex Rainert officially launched Dodgeball in mid-2004, the service quickly built a base of thousands of users in 22 U.S. cities. But had Dodgeball gone live a few years earlier, Crowley doesn't think it would have been as successful.

"Early on, it was so hard to get people to try things. No one was using their mobile Web browser; you couldn't text-message between carriers. A lot of those things are starting to resolve now," he says. "I joke that one of the points where we knew Dodgeball was going to work was when my mom started sending me camera-phone messages, because it was easier than calling me. If my mom has this stuff figured out, then you know it's ready for prime time."

Google helped warm up the crowd. Its two-year-old Web mail service, Gmail, blew away the competition in bringing desktop-like functionality to an online application. (The heaps of free storage Gmail offers has also helped it build a huge, fervent customer base. Google doesn't disclose its Gmail user count, but analysts estimate it's in the millions.)