Forget the Rotary Club: You can now build your professional network online. A service called LinkedIn works this way: You sign up and invite your contacts to join you by registering on the site. They, in turn, invite their contacts, and so on, with the goal of establishing a large network. LinkedIn founder Reid Hoffman says the key to his site's viability is its recognition that the Internet is a pretty sketchy place. LinkedIn only lets people contact you if someone you personally know vouches for them. Currently, the service has about 15,000 users (mainly VCs and techies) and is totally free. But Hoffman hopes to eventually charge a monthly fee of about $10 for people who communicate with members of the network who are more than four degrees of separation away.

...And Index People

Any old numbers stored in your cell phone? Plaxo, a new website from Napster co-founder Sean Parker, helps you keep up with constantly changing contact information. The program asks you to choose people from your Microsoft Outlook address book to send an e-mail asking for addresses and phone numbers. They can reply by e-mail or by going to the site. Information among fellow Plaxo registrants is automatically updated as it changes. And it's all free--though Plaxo plans to charge for a new version; Parker won't say how much. John Kinney, founder of Club One fitness centers based in California, is one Plaxo user willing to pay a reasonable fee. He uses the site to keep track of 5,000 personal contacts. "It really does make things so much easier," he says.