UlboraCMS is a self-contained CMS (no database needed) written in Golang. It uses a JSON datastore with content saved in both json files and in memory. You can download and upload a single binary backup file containing content, images, and templates as needed.
The easiest way to get Ulbora CMS is to use Docker.
You can build multiple templates with Ulbora CMS and switch between the templates through the administration screen.
New templates can easily be installed by zipping them as tar.gz files and following a simple upload process in the administration screens.