The new social networking players, which include Cisco and a multitude of start-ups like Ning, the latest venture of the Netscape co-creator Marc Andreessen, say that social networks will soon be as ubiquitous as regular Web sites. They are aiming to create tools to let ordinary people, large companies and even presidential candidates create social Web sites tailored for their own customers, friends, fans and employees.

“The existing social networks are fantastic but they put users in a straitjacket,” said Mr. Andreessen, who this week reintroduced Ning, his third start-up, after a limited introduction last year. “They are restrictive about what you can and can’t do, and they were not built to be flexible. They do not let people build and design their own worlds, which is the nature of what people want to do online.”

Social networks are sprouting on the Internet these days like wild mushrooms. In the last few months, organizations as dissimilar as the Portland Trailblazers, the University of South Carolina and Nike have gotten their own social Web sites up and running, with the help of companies that specialize in building social networks. Last month, Senator Barack Obama unveiled My.BarackObama.com, a social network created for his presidential campaign by the political consulting firm Blue State Digital.

Many of these new online communities cater to niche interests. Shelfari, a Seattle-based start-up, recently began a service to let book lovers share their opinions. This week it received an investment from Amazon.com.

Mr. Andreessen’s Ning, based in Palo Alto, Calif., is fashioning itself as a one-stop shop catering to this growing interest in social networks. Anyone can visit the site and set up a community on any topic, from the television show “Battlestar Galactica” to microbrew beers. Ning users choose the features they want to include, like videos, photos, discussion forums or blogs. Their sites can appear like MySpace, YouTube or the photo sharing site Flickr — or something singular.