Stefan Mileschin

Neptune OS is a Windows NT personality of the seL4 microkernel. It implements what Microsoft calls the “NT Executive”, the upper layer of the Windows kernel NTOSKRNL.EXE, as a user process under the seL4 microkernel. The NT Executive implements the so-called NT Native API, the native system call interface of Windows upon which the more familiar Win32 API is built. These are exposed to the user mode via stub functions in NTDLL.DLL (a somewhat redundant name if you ask me) with names such as NtCreateProcess. The NT Executive is also responsible for the Windows kernel driver interface (known as the Windows driver model), which includes functions like IoConnectInterrupt and IoCallDriver. On Windows these are loaded into kernel mode and linked with the NTOSKRNL.EXE image. On Neptune OS, we run all the Windows kernel driver in user mode and they communicate with the NT Executive process via standard seL4 IPC primitives.

https://www.osnews.com/story/134603/...4-microkernel/