Pico is a free and open source CMS that built with PHP. It simple, there is no setup and work fast. It uses flat-files as the database.
The contents are created in .md files. You simply create .md files in the “content” folder and that becomes a page. The Text files are marked up using Markdown. you can be edited in your favorite text editor.
Pico uses Twig for it’s templating engine For the designing/theming.