Contao

Contao is an open source CMS (content management system) built for developers and agencies who need to create accessible, secure, and maintainable websites. It separates content management from layout using a template-based approach and a structured data model, rather than dragging and dropping in a block editor. The system outputs clean, semantic HTML by default, which helps with SEO and meeting accessibility standards like WCAG.

Created originally by Leo Feyer and now maintained by the Contao Association, the system runs on PHP and supports MySQL or MariaDB databases. It includes a built-in news and newsletter module, calendar, form generator with conditional logic, and a user rights system down to individual fields. The back end interface is entirely customizable and supports multiple languages. Developers can extend it using the Symfony framework components it is built on, including Twig for templates.

The project is dual-licensed under LGPLv3 and a commercial license, though the core is open and free. Contao has a strong community primarily in German-speaking Europe, with official documentation in English and German. It is well suited for agencies building custom sites without relying on bloated page builders.