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 >5x increase in throughput for Facebook compared with Zend PHP 5.2.
The latest information is available on the wiki.
HipHop VM is licensed under the PHP and Zend licenses except as otherwise noted.
Before changes can be accepted a Contributors Licensing Agreement must be signed and returned.