At a bar in Washington, D.C., last week about 100 people filled a back room. As they flowed in, they found seats, introduced themselves to the others at the table and promptly started sharing their opinions, some passionate and some subdued, on one pressing issue: health care reform.

What drew them to the event? Not the hope to voice opinions to an elected official. Not the desire to protest or rally. Just the opportunity to learn and engage with a local community, fueled by the type of "do it ourselves" political activism found on Meetup.com.

Individuals have long used the site to host local meetings related to any topic -- from Indian food to education policy -- though it wasn't until the grassroots-style success of the Obama campaign that Meetup reached its highest levels of use and its first month turning a profit, CEO Scott Heiferman said.

The core idea behind the site, creating an online platform where groups of people with common interests can find each other, seems tailor-made for the type of grassroots activism that many people want to be a part of on current political issues, like health care reform and climate change policy.

Alexander Moll, a citizen participation consultant, organized last week's health care forum, sponsored by the National Issues Forum. He spread word about the event through Facebook.com, my.BarackObama.com and Meetup.com, but he thinks Meetup is the most effective site available for bringing out crowds to his events.

"I still think Meetup is underrated comparatively," said Moll, who started using the site about six years ago, shortly after its launch. "Meetup has more of a suite of tools for organizing people."

Heiferman thinks the site continues to attract more and more users -- it's up to nearly 6 million members and 180,000 monthly meet-ups across the globe -- because people are looking more to each other for information and dialogue, instead of media outlets. "That's a precursor to some really significant trends in how political lobbying and movements are going to happen," he said, pointing to the rise in grassroots campaigns for both candidates and issues.

Heiferman says the grassroots groups forming around causes on Meetup are different from the traditional interest groups that are associated with lobbying because the members don't just pay dues or make donations. Meetup users actively seek out groups, then do something to promote the group's cause on a regular basis. And because most Meetup groups aren't associated with an umbrella organization, the members take on true ownership of their issue.

That's why Alicyn Basse attended last week's health care forum organized through Meetup. She was tired of sitting in front of a TV and listening to political pundits talk about the legislation, and she wanted the opportunity to work out her own views on health care.

"I wanted to formulate my own opinions by hearing what's really going on," said Basse, who recently moved to D.C. and joined Meetup last month as a way to meet new people and get involved locally in the causes she cares about most.

Heiferman did not have political activism in mind when he and co-founders Matt Meeker and Peter Kamali launched the site in June 2002, but that soon changed. "A few weeks after we launched, that's when there were some supporters of Howard Dean crawling around the Internet looking for some ways to organize themselves," Heiferman said.

At first, the "Deaniacs" used the site to set up meetings in their communities, but in early 2003, the campaign saw the potential of a tool like Meetup for political campaigns and asked Heiferman how they could team up. Meetup soon provided, for a price, additional organizing tools for the campaign -- e-mail collection and messaging, a direct link from the campaign's Web site and reports about supporters' activities on Meetup. That's what helped Meetup turn a profit. Organizers are now regularly charged a subscription fee that varies based on the host's ambitions.

Still, the self-organizing formula isn't perfect. Because the political nature of a group isn't always evident by the group's name on Meetup, it can be difficult to find a meeting to attend. A search for "health care reform" in the Washington area, for example, only brought up four results. Heiferman says one of the improvements coming soon is a change to the search tool that will make it easier for individuals to connect by uncovering groups that are relevant but don't have the search term in their title.

"We've only really just scratched the surface of how easy it's going to be to organize online," he said.