[hnlmorg]

That’s arguably an easy task though because there is more commonality due to POSIX.

But there are plenty of examples of compatibility layers like this throughout computing history. WINE, cygwin, Linux compat, etc.

Microsoft even went down this road already in the 80s with Xenix before abandoning the idea of Unix.

The only novel part of WSL was the marketing folks

[AndrewDavis]

Microsoft had a POSIX personality on NT since its release in 1993.

https://en.wikipedia.org/wiki/Microsoft_POSIX_subsystem

Then with the release of XP it was replaced with: https://en.wikipedia.org/wiki/Windows_Services_for_UNIX