8:46 AM - More MACH
The MACH kernel went through several development forks from the CMU projects.
We have MACH 4 (UNIV of UTAH) and the LITES project from UNIV OF HELSINKI. Basically that just booted the Mach 4 development kernel on a FreeBSD 2.x userland and partition table.
http://www.cs.utah.edu/flux/mach4-i386/html/UK02p21-release.html
MACH 3 and lower of course.. original work
http://www-2.cs.cmu.edu/afs/cs.cmu.edu/project/mach/public/www/FAQ.html
GNU Mach along with GNU/HURD...
http://www.gnu.org/software/hurd/gnumach.html
Debian GNU/HURD distro
http://www.debian.org/ports/hurd/hurd-install
http://www.debian.org/ports/hurd/hurd-cd
(available on FTP) http://na.hurd.gnuab.org/pub/debian-cd/K8/
Of course there was the NeXT and now darwin/opendarwin implementations.
One thing of interest so far is the reference to single server vs multiserver mach kernels. GNU Mach is a multiserver kernel which appears to run multiple services to service requests. It seems similar possibly to dragonflybsd's abstraction but a little more so.