Jimmy Wales, founder of wikipedia, gave an interesting talk at eTech this morning.
Freely licensed encyclopedia, created and managed by thousands of volunteers. It was created in 2001. There are close to 500,000 articles in english, and over 1.5 million articles spanning dozens of languages.
Wikipedia has 350,000+ categories, based on a hierarchical tree structure.
Wikipedia is very popular, drawing more traffic than even the NY Times; there are over 500 million page views a month.
Based on the original idea of using the web to share information, wikipedia improves on single author web pages in that each entry is peer-reviewed and subject to correction by anyone viewing the site.