GRAV is an awesome open-source CMS that I've been using for years now. I use it to run this website, too!

GRAV can be used to build a statically served website that looks awesome in just seconds. It comes with an admin plugin for web-based content management, plugin and theme support as well as lots and lots of tools for customizing your install. Due to its static nature, it allows pages to pre-build themselves and provides great performance.