PHP supports different types of content management system softwares’ like Joomla, drupal, etc., all CMS softwares’ are open source.
PHP supports different types of security functionality like encryption and authentication, authorization etc.
PHP supports different types of editors to create functions and programs.
Zend organization is maintaining PHP, they introduced number of editions to work with PHP.
By using some third party tools we can develop stand alone applications with PHP but we cannot provide complete functionalities to that application because PHP is purely for web development.