The GNU Hurd is, together with the GNU Mach microkernel and the C library, the core of the GNU system. The Hurd is a set of servers running on Mach, which implement the basic system services like filesystems, network protocols, authentication, and process management. The system is user extensible and replaceable, but GNU libc provides a complete POSIX compatible programming interface on top of it.
The last version of the Hurd that was released 1997 has since been improved dramatically, so that everybody who is interested in trying out the Hurd should use the current development versions. Binary packages of the distribution are available in the Debian unstable archive, and can be installed conveniently, either over the network or from CD images. The complete binary distribution contains well over 2000 software packages on four CD images, including most GNU programs and other software that is part of the GNU system (TeX, XFree86, and more).
Because there are still stability problems and some important features missing, the Hurd system is in general not ready for production use yet, but it is usable as a development platform, and to some extent also as a desktop machine (as far as it provides the features the user needs). Also, the advanced functionality of the Hurd system (like, booting several independant Hurd systems in parallel) are working good.
Currently, development of the binary distribution has been stalled while we are undergoing an ABI change in the C library and the move to gcc 3.0. Also, the driver framework in the microkernel will be replaced by OSKit in the near future. So, there will be massive changes to the core system, which will improve the usability and stability of the system and have a measurable effect on the quality and size of the binary distribution when we resume its development.
Information about installation of the Hurd is available from the GNU Hurd web site, http://www.gnu.org/software/hurd/.