PHPDoc is a tool for generating API documention of PHP applications from source code. It greps the information from the source and takes the information from special PHPDoc comments to create a documention of functions, classes, package.php and modules.
Go to http://www.phpdoc.de/ to get further information and for a demonstration.
The complete PEAR project is documented using PHPDoc comments. If you want to see using examples of this comments, just take a look at the PEAR sources.