Zend Engine [SEP] license
been freely available under the Zend Engine License (although some parts are under the PHP License) since 2001, as part of the official releases from php.net, as well as the official git repository or the GitHub mirror. Various volunteers contribute to the PHP/Zend Engine codebase.
Architecture.
Zend Engine is used internally by PHP as a compiler and Runtime engine. 
PHP Scripts are loaded into memory and compiled into Zend opcodes. 
These opcodes are executed and the HTML generated is sent to the client.
heart of PHP, originally written by Andi Gutmans and Zeev Suraski. The first version of Zend Engine was shipped with PHP4. Zend sponsors some developers to actively contribute to the engine, while the main development of Zend Engine today comes from contributors to the PHP project.
Sponsored projects Zend Framework.
Zend Framework is an open-source, object-oriented web application framework written in PHP5 and licensed under the new BSD license.
Sponsored projects Simple Cloud API.
The Simple Cloud API is an open-source PHP API