If I mentally model such a thing myself, I end up with something that looks a lot like Classic (pre-OS-X) Mac OS. It's simplified and has just enough presence to properly host graphical applications. No taskbar, no notifications (or associated drawer), no self-populated launcher menu. File manager is spatial so it doesn't need a sidebar or navigation chrome. Multitasking is technically possible, but high-friction since the only way to switch between running apps is the little app switcher menu in the top right corner and becomes more cumbersome the more apps/windows you open. Included browser does not support tabs, only windows. Shortcuts to frequently used apps must be added intentionally (to your desktop as aliases/shortcuts or to the launcher menu).
This design strongly encourages singular focus without forcing it. If you want to have music playing in the background or need to open a browser window for research you can, but gravity is constantly pulling you back towards your task since the machine isn't pleasant to use for goofing off.