For the yanks and elsewhere, yes conkers is well known in Britain. You basically put a chestnut (but its a conker) on a string by making a hole in the middle. Take turns swinging them on the string, whoever's breaks is the loser.
It used to be great fun till it was banned/requires eye protection now. There's an opportunity there, someone could make a perfectly safe conker app. I'm sure that would adequately replace it. /s