We've tried a number of games and these are our favourites:
ksmiletris, by far the most successful I've used, fun for everyone.
ktron, the racing game, but slowed down, email me for the tar.
kpacman, I've yet to find a succesful cheat for our clients.
kasteroids, one client on the fire, another aiming.
kpat, too difficult for many. 'idiot' is a check on suit & numeracy.