HHVM is an open-source virtual machine designed for executing programs written in Hack and PHP. HHVM uses a just-in-time (JIT) compilation approach to achieve superior performance while maintaining the development flexibility that PHP provides.
HHVM runs much of the world’s existing PHP. Developers and hosts are adopting HHVM. We are aware of minor incompatibilities (please open issues when you find them), but we can run the top 20 Github PHP frameworks out of the box. The HHVM team, along with many wonderful community members, has made it a stated, high priority goal to run all existing PHP code existing out in the wild.