Software for PHP
Anchor CMS
Anchor is a super-simple, lightweight blog system written in PHP. Compressed, Anchor CMS weighs in at just under 250kb making it an extremely light weight content management system. With Anchor CMS, you can manage content in HTML or Markdown, depending on which you prefer. The content management is fully free and open-source and released under the GPL-3.0 License.
Flextype
Flextype is super fast headless content management system with an elegant architecture and built-in smart cache.
Subrion
Subrion is a PHP/MySQL based CMS & framework that allows you to build websites for any purpose. Yes, from blog to corporate mega portal.
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.
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.
PyroCMS
PyroCMS is a free and open-source Content Management System written in PHP on top the web development framework Laravel.
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.