Documentation-Robot--Drupal-6- is a project mainly written in PHP, it's free.
An attempt for automated basic technical documentation for Drupal 6 sites
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This module is an attempt to create basic automated technical documentation for Drupal 6 websites. The idea is to get lists of things like node types, views, modules/projects and user roles, and then rendering the list in various forms (such as a single page overview, Drupal book nodes, XML data, and what not).
There is currently a hook for collecting 'documentation items', and functions that collect and expose information about projects, modules (including patch files), user roles and node types (including rudimentary information about CCK fields).
The data is collected in Drupal form API format, and currently only displayed on a single page (admin/help/docrobot).