There was a folder for the Microsoft specific stuff, but looks to be removed now. However, all the forks of things are still there:
Code:
Windows NT 4.0: https://git.rip/Felony/windows-nt-4-source-code
Windows NT 4.5: https://git.rip/gravin/windows-nt-4.5-source-code
Windows 2000: https://git.rip/Felony/windows-2000-source-code
Windows 10 Shared Source Kit: https://git.rip/Felony/windows-10-shared-source-kit
Original Xbox: https://git.rip/Felony/original-xbox-kernel-source
Windows Research Kernel 1.2: https://git.rip/haniella/windows-research-kernel-1.2