Well, maybe invent isn't the right word....how about hack. Over at the Walker they needed a way to keep a live count of the people in an exhibit gallery that has multiple entrances.
Solution: two wirelessly networked iPod Touches. They just built a little web app that allows people at both entrances to add and remove people from the tally which is then stored on a remote webserver. Simple and genius. I could see this having quite a few evaluation uses beyond simply keeping track of gallery capacity.

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