Over at Lifehacker, a tutorial from Make shows how to make your own jockey box for chilling beer. For those unfamiliar with the term, jockey boxes are basically ice chests which sit between the keg and the tap. The beer flows through tubing, which is in ice or ice water, chilling the beer to a drinkable temperature.
They call this a “convertible” jockey box because you can remove the tubing and drop a mini-keg in. That sounds cool but I’ve never seen craft beer in a mini-keg so I doubt I would ever do that. As someone noted in the comments, you could also use this as a wort chiller for homebrew, which is something I would do. You would need some kind of pump, though.