Feature: Open Source
HTMLy

HTMLy is an open source databaseless blogging platform. The Flat-File Blog and Flat-File CMS written in PHP.
Mara CMS

Mara CMS performs a similar core function to 'Content management systems' like Drupal or Wordpress - although it differs in many fundamental aspects from those packages. Probably the most significant difference is its being file based instead of database dependent.
Middleman

Middleman is a static site generator using all the shortcuts and tools in modern web development.
Monstra

Monstra is a modern and lightweight Content Management System. It is Easy to install, upgrade and use.
Nibbleblog

Nibbleblog is a powerful engine for creating blogs, all you need is PHP to work.
PhileCMS

PhileCMS is a file-driven CMS. Powered By Markdown And Twig. But You Can Change That.
Singularity

Singularity is a simple (single PHP file), flat file CMS which marks up HTML using Markdown.
Wintersmith

Wintersmith is a flexible, minimalistic, multi-platform static site generator built on top of node.js.