Free and Open Source Software
Bootstrap CMS
CMS: Bootstrap - Opensource HTML/CSS/PHP and MySQL Content
Wagtail
Wagtail is a free and open-source CMS built on-top of Django and Python. The CMS is built by developers and for developers and provides a configuration-less solution to content management. Wagtail plays nicely with your existing tech, especially if that stack utilze Python and the Django web framework. Wagtail can be installed as a package in existing Django application and extends the Django Admin to be more suited for content management.
Portal CMS
Portal CMS is a free and open source content management system with a powerful integrated page...
Kotti CMS
Kotti is a high-level, Pythonic web application framework. It includes an extensible Content Management System called the Kotti CMS, offering all the features you would expect from a modern CMS. Kotti is built on top of a number of best-of-breed software components, notably Pyramid, SQLAlchemy, and Twitter Bootstrap.
WordPress
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.
Matrix CMS
Matrix CMS platform has been designed to provide a comprehensive and integrated solution to the product publishing requirements.
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.