Wikipedia
A Personal Statement about Wikipedia's Reliab, CNN.com - Wikipedia: The know-it-all Web site, First Monday - Phantom authority, self?selective r, Free-Definition: Wikipedia, Frozen North: How Authoritative is Wikipedia?, Guardian Unlimited - Wikipedia's success, ITworld.com - Chinese censors block access to Wiki, kuro5hin.org - Can an Open Content Encyclopedia Th, kuro5hin.org - Why Wikipedia Must Jettison Its Ant, kuro5hin.org - Wikinews And The Growing Wikimedia
Connected: An Internet Encyclopedia
The engineering, theoretical concepts, and organizations of the Internet (freely distributable).
Cunnan
An encyclopedia for reenactors of the Middle Ages and Renaissance period with a heavy slant towards members of the Society for Creative Anachronism.
dKosopedia
A collaborative project of the DailyKos community to build a political encyclopedia featuring liberal points of view.
Everything2
An extensively hyperlinked collection of facts, ideas, notes and humor to which anyone can add.
HierarchyPedia
A free-content encyclopedia that provides information on influential people and organizations throughout history.
Hierarchypedia
Open content encyclopedia on notable people and organisations throughout history.
Linpedia
A peer edited reference material for Linux and Open source software project where every term is properly defined; the project provides usable documentation that accommodates cross references and glossaries for all relevant terms in an article.
Metaweb
A project initiated by author Neal Stephenson as a resource first to annotate his novel Quicksilver, but based on the broader concept of a "metaweb" devised by Danny Hillis.
Musipedia
A collaborative music encyclopedia. Contains melodies and musical themes from classical, popular, and folk music. Can be searched based on the melody alone, either by whistling or singing, or by entering the gross contour as Parsons Code.
PlanetMath
Collaborative, peer-reviewed mathematics encyclopedia with TeX input, inspired by MathWorld (GNU Free Documentation License).
SourceWatch
A free encyclopedia of people, issues, and groups shaping the public agenda. It catalogs descriptions and details of PR firms, activist groups and government agencies as well as the criticisms that are made of these groups from different perspectives.
Technomanifestos Network
Collaborative resource on the history of computing and the Internet (GNU Free Documentation License), and the online companion to the book Technomanifestos.
Wikipedia Article - Nupedia
Nupedia was a public peer-reviewed general encyclopedia created by volunteer scholars, with resources for readers and contributors (GNU Free Documentation License). It can be considered to be Wikipedia's direct ancestor.