It's an OS made by Murena

Or to give you a more serious answer, it's also called /e/os. It's a deGoogled Android distro you can get preinstalled on some phones, including the Fairphone 6.

Basically, it offers a way for less techy folks to switch to a Google free Android OS, as you don't have to unlock bootloader, flash ROM, etc. Does cost an extra 50 euros for the privilege though.

MurenaOS is an operating system that can run on a Fairphone.