Sami is an API documentation generator. It uses a PHP file for configuration to give a very flexible way of tweaking the API generation, Twig for templating and a dependency injection container (Pimple) to let you override any internal class. It only works with PHP 5.3 (but it can generate documentation for PHP 5.2 projects). It uses the excellent PHP Parser project for PHP code parsing. You can also manage versions of your code to generate documentation for all of them in a single tree (without the overhead of re-parsing everything for each version of course).