A square what? Yup, watermelon.
Shaping vegetables and fruit is not really new but square watermelons are actually a practical solution for the Japanese refrigerator, or anyone's for that matter. http://theysmell.com/square-watermelons/
It could catch on here but you can bet it will not be at bargain basement prices. It actually takes some effort to push that watermelon into a cube. Prices in Japan can be up to $99 each!
Well..... maybe they don't push it into its' shape. They grow it into shape. Here is a project for the next few cold months. http://www.instructables.com/id/Grow-a-square-watermelon/
Watermelons take a lot of room to grow, so if you are a market gardener and want to get the best dollar for your watermelon acreage, would this help? I would bet square watermelons would sell out quickly at the farmer's market and should command a much better price. Double, triple or more?
Keep in mind that the watermelon you choose to try this with needs to be one that produces a melon only slightly larger than your shaping container. AND IT IS NOT A SPECIAL SEED, so don't get hooked by someone selling square watermelon seeds!
Read several articles on growing these and you will pick up some extra tidbits that will help.