There’s a new product released today by someone named Norman Freeman. It’s called ViralInviter, and it looks very clever. I’ve had this idea for a long time, but I haven’t yet seen any decent implementations of it. The idea is that your visitors can invite their friends to join your site with their email address books. Most people have nearly all of their contacts’ email addresses stored in a webmail service such as Gmail or Hotmail. By providing their login, you can automatically get their contact list and allow them to invite select people– or everyone– with a single click.