Originally Windows was written in assembly and ran on top of DOS, but since Windows 2000 and XP, it's been exclusively running on the NT kernel, which is written primarily in C, with some C++ in there as well.
There may be good examples out there, but I’d argue Atom isn’t one of them. VS Code was clearly intended to be a spiritual successor with MS branding IMO, it is a fork of Atom, and it is equally open source (MIT license).
Atom usage dropped off dramatically in favour of VS Code or the fully open source VS Codium, there's no point in Github writing it's own code editor when it's hosting a much more popular, more powerful, and equally open source editor in one of its repos.
Yeah, like I said, why would one company develop two direct competitors that are nearly identical instead of focusing on one?
Corporate consolidation tends to inheritly reduce competition / redundancy / resiliency, but that's not the same thing as an EEE strategy that is out here trying to extinguish open source projects in replace of their proprietary version. In this case Microsoft is shutting down one redundant (in their minds) open source project to focus resources on their other more popular one that is also being offered completely for free and open source under an MIT license.
You can even use VSCodium if you want none of the Microsoft branding (or fork it yourself to customize it, like many of the other tech giants do). This isnt open source being shut out so much as the industry standardizing on a specific open source project.