Currently, Debian is only available for Linux and kFreeBSD, but with Debian GNU/Hurd we have started to offer GNU/Hurd as a development, server and desktop platform, too.
The Hurd is under active development, but does not provide the performance and stability you would expect from a production system. Also, only about three quarters of the Debian packages has been ported to the GNU/Hurd. There are still a few things to do before we can make a release, see the TODO list.
Until then, you can participate in the development if you want. Depending on your experience and time commitment, you can help us in many different ways. For example, we need experienced C hackers to develop and implement new features and to fix bugs and debug the system. The Failed page shows the list of failing packages and a summary why. If you are not very experienced in C programming, you can still help: Either by testing the existing systems and reporting bugs, or by trying to compile some unported software you have experience with. Also writing documentation is important, or maintaining the web pages.
Porting packages is quite trivial most of the time, there are just a couple of traps that they can fall into, a list of common issues is available.
How do I join?
To start with Hurd development, you should install Debian GNU/Hurd and get used to it. Also, join the mailing lists and try to get a feeling for the state of the development. Offer your help, and we will tell you what is needed to do.