Xen == X# == Comega;
Looks like Microsoft Research picked up the ball and has released a version for people to play with.
Site is here [0], download is here [1].
Thanks to BobB at DM for the heads up.
[0] http://research.microsoft.com/Comega/
[1] http://www.research.microsoft.com/research/downloads/default.aspx
End of line.