DokuWiki: An elegant and lightweight wiki engine

Created as a simple solution for managing documentation, DokuWiki has evolved into a powerful and flexible wiki suitable for most tasks involving collaborative editing. DokuWiki doesn't use a database back end (all pages are stored as plain text files), which makes it easy to install and maintain.

Its access control list feature offers a user-friendly and flexible mechanism for restricting access to certain pages and namespaces. You can also extend DokuWiki's default functionality using plugins, and there are hundreds of plugins to choose from.