I think any OS can be divided into a "backend" that deals with the hardware and a "frontend" user-level applications with a UI. The backend is mostly similar everywhere, while the frontend is what the general public typically perceives as the "OS". It's hard to see anything truly new in the "invisible" backend, but the frontend changes with every update (Windows, Mac, Linux etc). ACPU OS is a good example of this, where the backend can be a different OS, an emulator or actual hardware, while the frontend remains the same across all execution environments. https://www.acpul.org/blog/so-fast