Open Source Content Management Software
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.
CushyCMS
CushyCMS is a FREE hosted content management system that's actually easy to use, fast to setup and doesn't require programming skills.
FeinCMS
FeinCMS is a bare bones content management system written in Python on-top of the web framework Django. The CMS is built to know nothing about your content, and includes an admin interfaces that can handle content types. It lets you reorder page content blocks using a drag-drop interface, and you can add as many content blocks to a region (sidebar, header, etc) as you want. FeinCMS was built this way to allow for maximum flexibility, where developers, designers and content managers can create a unique site, tailored for their type of content and future patterns.
October CMS
October is a free, open-source and self-hosted content management system written in PHP on top of the framework Laravel. The CMS features a universal extendable dashboard, inspector, reusable CMS components and a plugin system that can be used to extend functinality of your website. The plugin store contains thousands of community-made plugins that can either be purchased or installed for free. As a data store, October CMS supports MySQL, PostgreSQL and SQLite.
GeniXCMS
GeniXCMS is a Simple and Lightweight CMS and Framework. It's PHP Based CMS. Free and Opensource.
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.
Flextype
Flextype is super fast headless content management system with an elegant architecture and built-in smart cache.
LightCMS
Easily Create Fantastic Websites with Highly Customizable Templates & Intuitive Tools for...
Agility CMS
Agility CMS is a cloud-based content management system for building and managing responsive websites and apps.