TWiki

TWiki is an open source (GPL) wiki program. The software is positioned as a "flexible, powerful, easy-to-use enterprise collaboration platform" and runs in the Perl environment.
TWiki has been developed since 2001, with a major version released approximately every year. The latest stable version is version 2004-9-4, and the latest beta version is version 2006-01-31.
Twiki is used by many large commercial companies, such as Yahoo, SAP, Motorola, Wind River, etc.
The content of TWiki's official site is copyrighted. The TWiki name is a registered trademark owned by Peter Thoeny. Content contributions belong to Peter Thoeny and its contributors.

Features of TWiki:
TWiki is a full-featured wiki system focused on giving structure to the website. All pages are automatically classified into TWiki Web, making it easy to create collaborative groups. People with programming skills can use variables to create dynamic pages, such as tables of content, or pages with embedded search results.
Easily customizable and extensible allowing page editing: Darkar version already supports WYSIWYG editing.
Access control: A refined authorization mechanism allows administrators to restrict read and write access rights to different departments.
TWIKI is a formatting engine that does not require any database and is completely based on file directories.