I find the story of the Hurd really interesting because it goes much beyond the discussions about the kernel, GNU, Free Software, Linux and computers in general. It involves people, relationships, strategies, decisions, work, commitment, random events and many other things that make life so exciting. It is important to see the mistakes of this project to try to avoid them and it's much easier to spot them now that we know the outcome. I believe that the GNU people did the best they could under the circumstances but, of course, they couldn't predict the future.
Can you tell the difference between a kernel and an operating system? Aren't they both standing between the humans and the machines? Although the term "kernel" is well defined, an "operating system" is not and most of the time there is no reason to differentiate an OS from its kernel. It is interesting to do that though in order to know the difference between Linux and GNU/Linux.
GNU is an operating system that is developped by the GNU prject. The GNU project is part of the Free Software movement and aims to build a free (as in freedom) operating system. The project consists in gathering people around the world to develop software that is freely available and can be modified and distributed without restrictions. To license GNU, Richard Stallman created the GPL (General Public License) that is widely used today to license all sorts of Free Software. This license grants to the developer and to the users four basic freedoms to use, share, modify and distribute software.
One of the most interesting things about the Free Software world is the psychological stories at play and the human tragedy that unfolds before your eyes as you discover it.