In fact, even this is called CasaOs, it’s not un OS, but some kind of interface for functions, it looks.
Anyway, it is compatible with Debian, Ubuntu distros, and add very easy GUI to it. So when it’s added to a linux based home NAS, it can be quite useful.
I heard that they’re making a real OS named ZimaOS based on CasaOS interface.
Here is their homepage;
And their wiki
https://wiki.casaos.io/en/get-started
But it has very important problem. For now, it cannot treat RAID storages. You may need to use mdadm.