Grav - The modern open source flat-file CMS
HTMLy - HTMLy is an open source databaseless blogging platform. A Flat-File Blog and Flat-File CMS written in PHP prioritizes simplicity and speed.
BoidCMS - Flat file CMS for building simple websites and blogs.
WordPress - WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
GetSimple CMS - GetSimple is an XML based lite Content Management System.
BaferCMS - The fastest and the easiest way to edit content "in-place", while looking at the website.