For many years Microsoft Research worked on an entirely new OS, codename Midori (https://en.wikipedia.org/wiki/Midori_(operating_system)), and it actually went into the incubation phase (which is Microsoft speak for "This is no longer a research project. We are turning it into a product") Then it got cancel around 2 or 3 years ago … just before it otherwise would have become a beta.
Today, they are not working on a new OS AFAIK. They are working on something called Andromeda. They have been working on that for, I don't know, 4-5 years or something like that. It is not a new OS. It is windows 10, but they have turned it very very very modular. It has a new adaptive shell named cshell as its party trick. Andromeda is really about that shell. Not so much about the modularity.
The new shell, they are working on, can adapt to any screen size or form factor on the fly and enable Microsoft's wet dream: Turning a phone size device into a tablet sized device.
You know from sci-fi movies "stretchable screens". you have a small phone size device, you stretch it and suddenly you have a book/newspaper/something-with-a-bigger-screen devices. Then you squeeze it back into phone size and put it into the pocket.
Windows need a new shell for when those types of monitors become available and it is the redmonds wet dream to be the ones that comes with those devices.
You might have stumbled across articles lately that Microsoft is about to launch (or have cancelled launching) a new device with 2 screens that you can turn in to 1 screen and there by turning a phone size device into a tablet).
That is andromeda and apparently is has been delayed (or maybe cancelled. Who knows) because the software is not ready. The "not ready part" is this adaptable shell.
(https://www.windowscentral.com/microsoft-andromeda-everythin...)