zend-engine

A sampling profiler or a memory profiler for PHP written in PHP, which reads information about running PHP VM from outside the process. You can find performance bottlenecks or memory leaks of your scripts without changing the target script or loading extensions.

Research about the Zend Engine

The Zephir Parser delivered as a C extension for the PHP language.

JaM is a PHP monitoring system that supports storing PHP errors (events) into different storage backends

The C++ wrapper of zend engine

Zend Engine 3 Zephir Kernel

An alternative PHP engine written in Go.

NotMyFather is a PHP extension rootkit PoC