WikiWiki

WikiWiki - a collaborative software application, enabling web documents to be authored collectively using a simple markup scheme and without the content being reviewed prior to its acceptance. Often called Wiki for short.

A WikiWikiWeb is a collaborative hypertext document produced by a community of users by means of a WikiWiki tool.

The original WikiWikiWeb was established by Ward Cunningham, who invented and named the Wiki concept, and produced the first implementation of a WikiWiki server.

Ward's Wiki remains one of the most popular Wiki sites:

http://www.c2.com/cgi/wiki?WelcomeVisitors

The particular Wiki you are looking at is Wikipedia, an effort to write a complete encyclopedia from scratch, collaboratively. We're currently writing at a pace of about 1200 new pages per month, although it seems that the pace is actually accelerating.

You can search various wikis at once, including this and Ward's, using MetaWiki.