GNU/Hurd strikes back
Unlike the Linux kernel, the Hurd is not a “kernel.” In a way,
“Hurd” = GNU Mach (microkernel) + GNU Hurd (system servers) + GNU MIG (Mach Interface Generator)
are roughly equivalent to a “kernel.” The GNU Hurd is a herd of servers that implements many functions, including user authentication, binary execution, the file system, networking, and even /dev/null as a server separate from the kernel. There are currently 24 servers consisting of the Hurd.