HipHop VM (HHVM) is a new open-source virtual machine designed for executing
programs written in PHP. HHVM uses a just-in-time compilation approach to
achieve superior performance while maintaining the flexibility that PHP
developers are accustomed to. HipHop VM (and before it HPHPc) has realized
a > 5x increase in throughput for Facebook compared with Zend PHP 5.2.

HipHop VM is most commonly run as a standalone server, replacing both Apache
and mod_php.

WWW: https://github.com/facebook/hiphop-php/wiki