The Internet played an unprecedented role in rallying voters during this year’s election. In the aftermath of the election, Web 2.0 tools are continuing to play a role in other causes, astonishing long-time advocates with the power and speed with which it gets their message out.

The latest example is a series of international protests scheduled for Saturday in opposition to California’s Proposition 8, the gay marriage ban that passed on Nov. 4. Join the Impact, a Web site built the morning of Friday, Nov. 7, has rallied hundreds of thousands of people who are gathering this weekend in eight countries, 50 states and 300 cities.

“This is the potential of the Web,” said Ben Elowitz, chief executive of Wetpaint, a company that builds Web sites for individuals and companies and built one for Join the Impact. “When Web 2.0 started, people started talking about giving ordinary people a voice online. This is the pinnacle of giving people a voice online. And people are taking that voice and making it meaningful with a megaphone.”

Amy Balliett, one of the two original organizers of the movement, has organized local demonstrations and fund-raisers in the past the old-fashioned way, with fliers around town and word of mouth. She said she was astonished at the momentum and speed that Join the Impact has picked up from the Web.

She contrasted it with the Stonewall Riot of 1969, which was a turning point in the campaign for gay rights. “Had they had social media, had they had the Internet, we would have been able to accomplish a lot more already, because they would have been able to keep the message alive and keep the community going,” she said.

A week ago, Ms. Balliett, who lives in Seattle, received a call from a friend, Willow Witte, who was trying to organize a local protest against the passage of Prop 8 in Cleveland but was not getting much traction. They decided to form Join the Impact to rally people around the country, and set up a Web site Friday morning. By Sunday night, it was getting 50,000 hits an hour and the server crashed, “which was a bittersweet problem to have,” Ms. Balliett said.

She found a new Web host, Hostdango, which gave Join the Impact a bigger server for free. It crashed the next day, so Hostdango gave them an even bigger one. On Monday morning, Ms. Balliett got a call from Wetpaint, offering to build her a new site where supporters could add their own information about protest locations and times.

Wetpaint lets individuals build Web sites for free and companies build them for a fee. HBO, Dell and T-Mobile have all built sites on the network. In four days, Join the Impact has become Wetpaint’s most-visited site, with over 1 million views.

“When I started this company, this is what I wanted to see,” said Mr. Elowitz of Wetpaint. “This generation of 20- and 30-somethings is so plugged in online that they’re really learning to use online as a platform for organization and activism.” His work has touched on marriage in the past — he is a co-founder of Blue Nile, the online diamond retailer that specializes in engagement rings, which is now a publicly traded company.

Join the Impact is also on Twitter and Facebook, which are also helping to “drive the masses,” Ms. Balliett said.

After the Saturday protests, the week-old organization will keep harnessing the power of the Web to fight for equality, she said. Next up: they are planning a “day without gays,” when they will encourage gay people to stay home and not contribute to the economy.