WordPress is an open-source PHP CMS released in 2003 that powers roughly 43% of all websites, the top share of any CMS. Its 60,000+ plugins and 12,000+ themes make it the common foundation for blogs, business sites, and ecommerce.
Grav is an open-source flat-file CMS developed by the RocketTheme team, with no database, Markdown file storage, a free MIT license, lightweight deployment, and multilingual support for documentation and light content sites.
Fork CMS is an open-source lightweight PHP content management system from Belgium, first released in 2010, known for modular extensions, multilingual support, and quick deployment, suited to small and medium business websites and localized sites.
Textpattern is a lightweight open-source PHP CMS released in 2003, known for semantic templates and Textile typesetting with a small footprint and SEO-friendly output, suited to personal blogs and light content sites.