Automad is a open source flat file CMS.
Baun is a modern, lightweight, extensible CMS for PHP.
Fast, Simple, Extensible and Flat-file CMS.
DodgerCMS is a static markdown CMS built on top of Amazon S3.
Grav is a modern open source flat-file CMS
Jekyll is a simple, blog-aware, static site generator.
Middleman is a static site generator using all the shortcuts and tools in modern web development.
PhileCMS is a file-driven CMS. Powered By Markdown And Twig. But You Can Change That.
Pico is a stupidly simple & blazing fast, flat file CMS.
Sculpin is a static site generator written in PHP.
Wintersmith is a flexible, minimalistic, multi-platform static site generator built on top of node.js.