Friendster, Sunnyvale, Calif.: Popular free site is primarily for social, rather than business, networking.
ItsNotWhatYouKnow , Indianapolis: Free business networking.
LinkedIn, Mountain View, Calif. : Free site lets members construct their own online circle of contacts, connect to other users' similar networks, and search for business contacts up to three "degrees" away.
Meetup, New York City: Free site organizes monthly in-person meetings for people with shared business and social interests in hundreds of cities of worldwide. Business topics range from general ("small business") to specific ("accounting," "sales," "work-at-home moms").
Orkut: Free offshoot of Mountain View, Calif.-based Google offers social networking; in beta testing with limited access at this writing.
Plaxo, Mountain View, Calif.: Offers a variety of options for finding contacts and managing information.
ReferNet, Sunnyvale, Calif.: Free site lets small- to midsized businesses network and make referrals.
Ryze, San Francisco: Free site offers business networking based on shared interests.
Tribe Networks, San Francisco: Free site offers business and social networking in discussion forums based on shared interests.
ZeroDegrees, West Hollywood, Calif.: Business networking site; currently compatible only with Internet Explorer running on a Windows platform.
The following companies provide software and services that analyze data in e-mail or other systems, allowing companies and individual users to automatically build private secure networks of contacts.