Free Software for Web
Grav
Grav is a modern free and open source flat-file content management system. With Grav, you can publish content and build sites in a fast, flexible and simple manner with the file-based web platform. Grav requires zero installation and is just an zip archive that can be extracted to start using the CMS. Grave also comes with a powerful package management system that allow you to extend the feature set of Grav CMS. With the package management system you can install and upgrade themes and plugins written specifically for Grav. The software is written in PHP and released fully free and open-source under the MIT License.
Exponent CMS
Exponent CMS is a notable free and open source content management system that contains its own independent modular software framework of enterprise level.
Quanta CMS
Quanta is a free, open source Content Management Framework thought for programmers and used for the creation of new-generation websites and applications.
Textpattern
Textpattern is an elegant content management system that is free, open source software. Textpattern is designed to be flexible with powerful tag-based templates that allow you to structure data and manipulate content. The content management system itself can also be extended with the use of plugins, that allow anyone to improve core functionality or add new features. Textpattern already have hundreds of available community built plugins that can be used to improve your website today.
Django CMS
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.
PhpSQLiteCMS
phpSQLiteCMS - a simple & lightweight CMS
Storyblok
A headless & API-based CMS with an opt-in head and a visual editor. With Storyblok you can manage your content through an intuitive dashboard and access that data though the content delivery API, as nested JSON. Storyblok is an open-source software and can be used as such, but is also provided as a commercially hosted, cloud rendering service. As a front-end developer you can choose to work with any template engine, framework or system of your choice.
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.
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.
Superdesk
Superdesk is a state-of-the-art digital newsroom system that combines headless CMS functionality with powerful workflow features for an end-to-end news creation, production, curation and distribution platform. With Superdesk you can create and distribute content to any platform. All within a web-based dashboard that share many similarities with a regular newsroom, while providing remote-friendly workflows that will make journalist feel right at home.