It's based on ReactPHP and works best with applications that use request-response frameworks like Symfony's HTTPKernel. The approach of this is to kill the expensive bootstrap of PHP (declaring symbols, loading/parsing files) and the bootstrap of feature-rich frameworks. See Performance section for a quick hint. PHP-PM basically spawns several PHP instances as worker bootstraping your application (eg. the whole Symfony Kernel) and hold it in the memory to be prepared for every incoming request: This is why PHP-PM makes your application so fast.
More information can be found in the article: Bring High Performance Into Your PHP App (with ReactPHP)
http://marcjschmidt.de/blog/2014/02/08/php-high-performance.html Features
Performance boost up to 15x (compared to PHP-FPM, Symfony applications).
Integrated load balancer.
Hot-Code reload (when PHP files change).
Static file serving for easy development procedures.
Support for HttpKernel (Symfony/Laravel), Drupal (experimental), Zend (experimental).
https://github.com/php-pm/php-pm