Frustrated with some of the limitations the phpDocumentor tool has - mostly dealing with the memory issues - Mike van Riel has introduced how own tool that works similar but takes better advantage of advancements in PHP to keep things bit more manageable - Docblox.

Right before or during the Dutch PHP Conference 2010 the issue had arisen again and this time I was determined on solving it. In the end I chose to build a new Documentation Generation Application (may I coin DGA?) for PHP [...] With [a list of key] requirements written down in a small TODO file I started designing the new project (which at the time was still nameless) After spending some hours designing, coding, prototyping, designing, coding and testing is now the time to reveal the fruits of my labour: DocBlox

Currently the project is in a pre-release state but is quickly headed to a 1.0 release. The current codebase is completely able to parse files and output the results to HTML files. PDF support is planned for the future. You can find the current feature list here and can download/clone the latest source from it's github repository.