It's easy - just select the desired access level, copy this link and send it via email, instant message, etc.Link: Just a link to your wiki. Post this anywhere and people can ask you for the invite key.
(For my working definition of social network sites, see my blog)
1996
MediaBar set up as an operating system for location based theme restaurants. Faces input into system, multi-user activity, food and drink ordering
Microsoft's Hotmail is born
1997
June: The Big Network, a startup in Berkeley CA, launches MyPlace - family-oriented social networking with public and private areas for friends and family to gather. The private areas include chat, calendar, forums, link sharing, image uploading, and both public and private game rooms containing single- and multi-player games.