DokuWiki
DokuWiki is a wiki application licensed under GPLv2 and written in the PHP programming language. It works on plain text files and thus does not need a database. Its syntax is similar to the one used by MediaWiki.
History
DokuWiki was created by Andreas Gohr in June 2004. In July the first official release was published on Freshmeat (now known as Freecode). A big step in the development was the re-design of the parser and the renderer in January 2005. The new design was a big performance improvement and made DokuWiki usable for bigger documentation projects. It also prepared DokuWiki for an introduction of a generic plugin interface which simplified the development and maintenance of add-ons. A push of the level of awareness was the introduction of DokuWiki in the Linux distributions Debian in April and Gentoo Linux in July 2005. Since 2005, it has achieved significant usage.
Main features
More complete documentation of the above, as well as other features can be found on the feature list on the official web site.