You probably know the game of flashlight-tag. You just run around in the dark on a campsite. You hold your flashlight and try to shine it on one of the other kids, without the other kids shining their lights on you.
I wanted to make this game electronic. The Arduino is my first choice, but would be a bit expensive. I would need one Arduino for each player. The next clip from "Make:" gave me the idea of using a cheap ATtiny:
I want the thing to register a "hit" and show this for a couple of seconds and count the number of "hits". That is all it has to do.