	Yes, it is.  It is available at ftp.ctr.columbia.edu, probably
in pub/xkernel.  

	In response to the earlier gentlemans question, you could
theoretically recompile xkernel on a sun4.  The binaries available are
for the sun3/50, but the author says it could be used on most
architectures, and he does have a 'do-it-yourself' type distribution.

	We use Xkernel for about 7 machines here.  email me if you
have any questions I can help you with...