HipHop Virtual Machine, a JIT replacement for PHP - main runtime

 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.
 .
 For the majority of your programs HHVM should be a drop-in replacement for
 the usual PHP interpreter/engine.