If you don't know Kalaha by name you might know it once you start playing. It's a very old puzzle game that, in its original format, uses small clay cups and little balls. These are arranged in two lines of six with bigger cups at either end. You must move the balls in each cup towards your goal. If you have six balls in one cup, you move them all so that a ball fills each of the next six cups along. A ball must fall exactly in the goal to stay there. If a single ball falls in an empty cup it moves into the goal and takes all the balls in the opposite cup. If it sounds difficult, it's not once you've had a few plays.
What is difficult is the computer. It's a frighteningly tough opponent. So far I have won once out of ten goes. And I'm not stupid. The computer is also very fast so you can whizz through the games and if it looks like you're going to lose yet again you can hit 'new game' and begin again. It's a simple game and a very good challenge which is infuriatingly addictive.