From the website...
Everything2 is similar to a wiki with FreeLinking BracketedLinks in that it is a pretty random collection of user-generated nodes that are interlinked using special syntax. It is different in that the structure of the text is more free (ala RawHtmlWiki) whereas WikiSyntax is very constrained, and the trust model is based on more HardSecurity like voting and rating, whereas a wiki uses more SoftSecurity. Everything2 also maintains active GodKings, for better or worse.
Like all ideas that kind of went somewhere on the 'net, a company, http://everydevel.com, has started to sell it. They call it the EverythingWebSystem and it has seemingly grown beyond Everything2, and several other (very different) sites .
Useful ideas that have come out of Everything2:
Everything2 is also interesting in that it has vigilantes actively seeking out copyright violators and reporting them. Some large flamewars have ensued. Of course, this is similar to people baiting others with [kiddie porn on Gnutella].
E2 also has a written policy that discussion about E2 is boring and pointless, and therefore 'nukable'. Debating editorial decisions and policy is automatically nukable under the above policy.
Copyright of articles on E2 rest with the author of the material.
Finally, its font size is way too small. [-- Though if you have a user account, it supports site themes, often with other (or even customizable) font sizes]
E2 used to disallow HTML links to other sites. This is no longer true. E2 now allows HTML links to other sites, albeit in a somewhat roundabout manner: one must click on the link and then click on another link, due to the vagaries of the internal linking system on the site. This was settled upon as the best solution to the problem by the E2 community.
Some people like to compare WikiPedia to Everything2. Most people familiar with both communities reject such comparisons.