The Hurd project is a loose community of people sharing a common interest in developing the Hurd kernel, which is the official kernel of the GNU operating system (see http://gnu.org ). When the Hurd was originally started in 1990, it was the last missing major component for a complete GNU system. Today Linux and other free kernels are available to fill this gap, and the combination of GNU and Linux (often incorrectly called just "Linux", see http://www.gnu.org/gnu/why-gnu-linux.html ) is in wide use. However, the Hurd is still interesting due to its unique design, better fitting the GNU philosophy than traditional monolithic kernels like Linux. The GNU GPL guarantees that all users of software published under this license get the legal permission to adapt the software they are using according to their wishes, and also get the source code and other tools necessary to put this permission to use. However, in traditional operating systems, the kernel and related low-level system software are protected from normal users, and cannot be easily modified; only the system administrator has power over these. The Hurd offers special mechanisms that allow any user to change almost all of the system functionality he uses, without affecting the rest of the system, and thus easily (at runtime) and without any special permissions. This ability to run subenvironments more or less independant from the rest of the system, can be classified as a very sophisticated lightweight virtualization approach. (See http://tri-ceps.blogspot.com/2007/10/advanced-lightweight-virtualization.html ) To offer these possibilities, the Hurd uses a true multiserver microkernel architecture. That makes it quite unique: The Hurd is the only general-purpose multiserver microkernel system in development today that is nearly ready for everyday use, and offering almost perfect UNIX compatibility. (More than half of the packages in the Debian repository are available for the Hurd.) All other existing true microkernel systems are either research projects not nearly complete enough for actual use, or limited to embedded systems and other special purposes, or both. Marcus Brinkmann and Neal Walfield from the Hurd project are working at the bleeding edge of microkernel operating system research. They have been in contact with the most distinguished researchers in that field from the L4 ( http://l4hq.org/ ) and EROS ( http://www.eros-os.org/eros.html ) / Coyotos ( http://www.coyotos.org/ ) microkernel operating system groups, and have written a couple of research papers ( http://walfield.org/ ).