Do you suck at pool? Well, this fancy system involving lasers and cameras shows you exactly where each ball on the table will go depending on where you're pointing the cue.
The whole thing is a little slapdash due to the budget limitations of the students who made it, but it's even more impressive when you consider the means they had to work with.
The limiting factor of our implementation was hardware. Unfortunately, projectors and web cameras with adequate wide angle lenses are priced outside of our means, and as such, we found that we needed to use key-stoning algorithms to correct for the fact that the camera was located in the corner of the room, rather than above the pool table, and had to use a very large mirror mounted to the ceiling to allow enough room for the projector to display on the whole table. The mirror introduced further issue insomuch as a mirror, glued to a large piece of plywood and hung upside down does not tend to be flat. And as a result, we had to account for those distortions in our code as well.
It's also worth noting that the code was designed using Microsoft Visual studio 2005 as an embedded OS project for an e-Box 2300.