Batflat - Lightweight, fast, easy, and free CMS.
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.
nCMS - Open source enterprise Java CMS engine
Grav - The modern open source flat-file CMS
Wagtail CMS - Django-based Content Management System.
Flextype - Flat-file content management system in PHP