phpDocumentor
phpDocumentor is the world standard auto-documentation tool for PHP. Written in PHP, phpDocumentor can be used directly from the command-line, or through its easy web interface to generate professional documentation directly from the source code of your PHP project. Support for linking between documentation, automatic class inheritance and generation of highlighted source code with cross-referencing to documentation are just a few of the features of phpDocumentor. Extensive templating allows the creation of documentation in 15 different HTML qualities, in Adobe Acrobat PDF format, in MS Windows Helpfile CHM format, and in XML DocBook format for PEAR package documentation at pear.php.net.