In short: just say NO TO DRUGS, and maybe you won't end up like the Hurd people. —LinusTorvalds
The GNU Hurd (see Hurd about the expansion of the "Hurd" acronym) is the GNU project's replacement for the Unix Kernel. The Hurd is a collection of servers that run on the Mach microkernel to implement file systems, network Protocols, file access control, and other features that are implemented by the Unix Kernel or similar kernels (such as Linux). Each server runs independently in user mode, with only the minimum permissions necessary for its job. DeviceDrivers can run with user privileges and even load their own servers without rebooting or affecting the stability of other servers or other users on the system or requiring SuperUser privileges to do so.
This differs from monolithic kernel designs such as Linux, where all of the code runs in Kernel space as a SuperUser; the downside is vastly increased complexity.
Hurd