ImpressCMS

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SilverStripe

PyroCMS is a free and open-source Content Management System written in PHP on top the web development framework Laravel.

WordPress powers roughly 30% of all web pages online. It's a free and open source CMS designed and developed for self-hosted publishing by Automattic, Inc. The software is written in PHP and utilize either MySQL or MariaDB as a database, and is compatible with most web hosts. Wordpress includes a plugin architecture and a templating system that can be used to extend and customize your website. These are commonly known as WordPress plugins and WordPress themes and make up a whole open source and commercial eco-system where anyone is free to create products for the platform. 

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.

Joomla is a free and open-source content management system written in PHP. The CMS is built entirely by volunteers from all over the world and has a strong community that provide educational resources, and extensions. 

Django CMS is a free and open-source content management system build on the Python web framework Django. With Django CMS, you can create your own website or blog in a matter of minutes which is easy to maintain far into the future. If you are a developer utilizing the Django framework you can integrate Django CMS into an exiting Django application and take advantage of it's publishing and editing features.

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.