Viengoos is a research kernel, designed and written by Neal Walfield.
As of late 2009, the project is on hold, due to time constraints.
Viengoos is not really meant to be a successor to Mach. It is highly experimental; some of the techniques it employs, in particular, those related to and IPC, are unproven. These were motivated by shortcomings in Mach as well as current operating systems. A research system is unlikely the best base for a product. A better approach is to view Viengoos as an experimental platform whose goal is to explore solutions to some of the issues uncovered by the Hurd. Knowledge gained can then be integrated into something like Mach.
The source can be downloaded from the viengoos.git repository, cf. http://git.savannah.gnu.org/gitweb/?p=hurd/viengoos.git. You can check it out using, for example:
git clone git://git.sv.gnu.org/hurd/viengoos.git
Then update to viengoos-on-bare-metal
cd viengoos git checkout -b viengoos-on-bare-metal origin/viengoos-on-bare-metal
viengoos-on-bare-metal is the current development focus.
Discussion should be held on the l4-hurd mailing list.