MediaWiki is the collaborative editing software that's designed to handle a large number of users and pages without imposing too rigid a structure or workflow.

DokuWiki is a standards compliant, simple to use Wiki, mainly aimed at creating documentation of any kind.

Tikiwiki is a full featured Free Software (GNU/LGPL) Wiki/CMS/Groupware written in PHP and maintained by an active international community.

A very popular PHP Wiki based on UseModWiki, with many features added.

coWiki is a sophisticated but easy to use web collaboration tool that helps you and your co-workers to create and organize web documents, weblogs and knowledgebases or any other document structures directly in their HTML browser.

Wacko Wiki is a slight and handy Wiki-engine based on Wakka Wiki 0.1.2 (latest Version).

ErfurtWiki is an implementation of the WikiWikiWeb hypertext system written in PHP.

YaWiki is "Yet Another Wiki for PHP".

Foopad is a free hosted wiki service featuring a very easy to use interface.

DocBookWiki can display DocBook documents online. DocBookWiki converts docs on the fly, so that the format will still be XML (DocBook).

A lightweight WikiEngine powered by PHP and MySQL.

PhpTiddlyWiki is a brand new kind of Wiki. It combines the awesome front-end of TiddlyWiki with a PHP/MySQL backend.

PmWiki is a WikiWikiWeb system developed by Patrick Michaud in the PHP scripting language. PmWiki has been primarily designed as a tool to support easy, collaborative authoring and maintenance of web sites.