Found this using StumbleUpon™. Created by playr.co.uk. Totally addicting. Single games are quick, the rules are fairly simple to pick up, and once you learn it you can play it off line with six normal playing dice, a friend, and a piece of paper for scoring.
(I would link the full SWF here, but free WordPress accounts can’t upload Flash files. Or if they can, I’m not privvy to those deep dark secrets… leave comments on how to do it if you know.)