Statamic

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Backdrop CMS

Kirby is a flat file content management system written in PHP. Kirby adapts to any project and can be used by developers, designers, creators and clients to create websites for businesses and personal use.

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.

WonderCMS is the smallest flat file content management system. The CMS is built with PHP and has been developed since 2008. No initial configuration required to setup the WonderCMS, the installation is straight forward and simply requires you to unzip and upload 5 files.All data within WonderCMS is structured as JSON format and the flat file nature of the content management system also allow you to migrate hosts easily by transfering files across, no database migration required.

Squidex is 100% open source headless CMS, built by passionated developers. With Squidex both individuals and organizations can handle content for the new web with ease. Squidex modular platform allows users to create content APIs that can be consumed by any frontend framework or technology in a matter of minutes. The framework itself can also be extended and tweaked to suite individual use-cases. Squidex is provided as a fully open source software released and free of charge, for the self-hosted community edition. For organizations that want to get up and running fast, commercially hosted solutions are provided.

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.