Grav is an easy to use, yet powerful, opensource CMS that requires no database. In a nutshell, installing Grav is a matter of unzipping the file. It is fast, has sophisticated caching, and a light footprint for optimal performance.
Automad is a file-based flat CMS and template engine. It is designed to be fully portable without any dependencies on databases or fixed locations and doesn't require any complicated setup process. All data gets stored in a human readable form.
FlatPress is an open-source standard-compliant multi-lingual extensible blogging engine which does not require a DataBase Management System to work. You don’t need MySQL because FlatPress stores all of its content on text files.
GetSimple is an XML based lite Content Management System. To go along with its best-in-class user interface, we have loaded it with features that every website needs, but with nothing it doesn't. GetSimple is truly the simplest way to manage a small-business website.
Pico is a flat-file, PHP-based content management system. There is no administration backend or database to deal with. You simply create .txt files in the 'content' folder and that becomes a page.