The Hurd is not the most advanced kernel known to the planet (yet), but it does have a number of enticing features:
it's free software
Anybody can use, modify, and redistribute it under the terms of the ?GNU General Public License (GPL)
it's compatible
The Hurd provides a familiar programming and user environment. For all intents and purposes, the Hurd is a modern Unix-like kernel. The Hurd uses the GNU C Library, whose development closely tracks standards such as ANSI/ISO, BSD, POSIX, Single Unix, SVID, and X/Open.
it's built to survive
Unlike other popular kernel software, the Hurd has an object-oriented structure that allows it to evolve without compromising its design. This structure will help the Hurd undergo major redesign and modifications without having to be entirely rewritten.
it's scalable
The Hurd implementation is aggressively multithreaded so that it runs efficiently on both single processors and symmetric multiprocessors. The Hurd interfaces are designed to allow transparent network clusters (collectives), although this feature has not yet been implemented.
it's extensible
The Hurd is an attractive platform for learning how to become a kernel hacker or for implementing new ideas in kernel technology. Every part of the system is designed to be modified and extended.
it's stable
It is possible to develop and test new Hurd kernel components without rebooting the machine (not even accidentally). Running your own kernel components doesn't interfere with other users, and so no special system privileges are required. The mechanism for kernel extensions is secure by design: it is impossible to impose your changes upon other users unless they authorize them or you are the system administrator.
it exists
The Hurd is real software that works Right Now. It is not a research project or a proposal. You don't have to wait at all before you can start using and developing it.