Free Software for PHP
TYPO3
TYPO3 is a free and open-source content management system written in PHP. The CMS is released under the GNU General Public License which makes it free to use for commerical and non-commercial projects alike. TYPO3 can run in most hosting environements and provides an easy way for people to write, manage and publish content online.
SilverStripe
Silverstripe CMS is designed to be simple to learn and easy to use. Whether updating a page or publishing multiple pages on a large scale site. Give access to edit only specific areas of your site. Architected to safeguard your data from malicious activity or data-loss, even while scaling up complex sites.
ExpressionEngine
ExpressionEngine is a flexible, feature-rich content management platform that empowers hundreds of thousands of individuals and organizations around the world to easily manage their web site. ExpressionEngine has a large community of developers that make add-ons that extend the system capability. With ExpressionEngine add-ons, no matter the task, you'll have a solution.
PyroCMS
PyroCMS is a free and open-source Content Management System written in PHP on top the web development framework Laravel.
CMS Made Simple
CMS Made Simple is a free and open-source content management system that offers an easy to use interface for end users, while maintaining a powerful backend for developers. CMS Made Simple is written in PHP and got an extensive API and custom modules. The CMS also utilize the Smarty templating engine that can be used to customize sites with HTML, CSS and PHP.
Drupal
Drupal is a free and open-source CMS written in PHP. Drupal is used for creating website for businesses, political parties and governments. The CMS currently powers 2% of all websites on the internet.
Batflat
Batflat is fast, database-less CMS written in PHP. Batflat weighs in on 1024 kilobytes and it has all features you have come to enjoy from other content management systems like WordPress. You can also download or create your own extensions for Batflat, allowing you to build features on top of the core and create unique experiences for the end-user.
Tiki Wiki CMS Groupware
Tiki Wiki CMS Groupware is a free and open-source content management system and Wiki software. Tiki has been downloaded over a million times by businesses, governments, non-profits and individuals worldwide to take advantage of its flexibility and customizability to deliver a broad range of web applications and wikis.
Hack
Developed by Facebook as free and open-source dialect of PHP, Hack is a programming language for the HipHop Virtual Machine. Hack is licensed under the MIT License and allows developers to use both dynamic typing and static typing.
ownCloud
With ownCloud, organizations can collaborate and be more production on their own secure enterprise file sharing (EFSS) platform. The ownCloud platform is self-hosted and allow for secure file sharing within an organization. The platform can be hosted on premise or on a cloud instance, controlled by the organization. The software is written in PHP and Javascript and is fully open source, released under the AGPLv3 license. ownCloud can run on most server hardware and operating systems, and the client for accessing ownCloud is available for Android, iOS, macOS, Linux and Windows.