The oldest public wiki (the Portland Pattern Repository) was created in 1995, and remains active as of early 2002. You can visit the PPR at Wiki:WelcomeVisitors?
Wikis are a unique and interesting way of organizing a web community.
Wikis are fabulous for software development groups to communicate by. - JasonBedunah?
Q: I don't get it? What the hell is a wiki? What if someone decided to erase, then what?
A: A Wiki is a website that is collaboratively edited by its users, including the ability to alter text written by other users. Wiki uses revision control to prevent abuse and track changes, so if someone decides to "erase everything" it's trivial to "revert" back to previous good version of the "erased page". It's easy to monitor for abuse with the RecentChanges? link. If someone is attempting to repeatedly abuse the system, their IP address can simply be blocked.
[Wiki:BoLeuf? Bo Leuf] and [Wiki:WardCunningham? Ward Cunningham] wrote a book that tries to explain it all: The Wiki Way, ISBN 0-201-71499-X (alternate, search).
Q: Why isn't the complete web 'Wiki'?
A: In today's society there is still a need for static boring web-pages. Wiki has only yet patched a small part of the web.