www.kraytracing.com

Here's a couple of links to get you going with kray:

This is one helluva long thread on Newteks forum:
http://vbulletin.newtek.com/showthread. ... 461&page=1

and here's a official site with couple of tutorial files and manual:
http://www.kraytracing.com/index.php?subpage=1

If you find any more please post them...