PEAR_Size started as a php script that was born of a need to determine if there were any large pear packages installed that could be removed to free up space; it is analagous to the unix command df - this tool lists how much filespace each installed package consumes; also a subset of packages can be specified as can channels.

That script has evolved into a reusable set of classes that can be used from your own code and can render its report into HTML, XML, CSV and plain text formats. This is extensible so if required you could generate PDFs and possibly even charts of the data that is generated.