WonderCMS - WonderCMS is the smallest flat file CMS. Completely free, open source, privacy oriented for over 12 years.
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.
BaferCMS - The fastest and the easiest way to edit content "in-place", while looking at the website.
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.
Nibbleblog - Nibbleblog is a powerful engine for creating blogs, all you need is PHP to work.