RatOS is a preconfigured Raspberry Pi image that aims to make it as painless as possible to get Klipper, Mainsail and Moonraker up and running on your printer. It is developed and maintained by Mikkel Schmidt (miklschmidt#2036 on the Rat Rig Unofficial Discord) with help from the community.
Start by reading the Documentation
To prevent you have to deal with an entire build chain setup, \ simply fork this repository.
Enable the workflows in your fork and you are good to go. \ On each push you make, an image is build and uploaded as an artifact.
If you want or need to build locally please visit CustomPiOS. \ Especially "Build a Distro From within Raspbian / Debian / Ubuntu / CustomPiOS Distros"