On: SkiftOS: Simple, handmade operating system for the x86 platform

[pjmlp]

Darwin is also written in C++, unless you don't consider drivers part of the kernel.

Windows has supported kernel code in C++ since Vista, hence why VC++ has the /kernel option on cl.exe.

BeOS, Symbian, ARM mbed, Arduino, IncludeOS, Meadow, GenodeOS for example.

Yes the set of C++ features one uses on the kernel isn't the full language, neither is C when used on the kernel.