The obvious plan of attack when you're building a stool is to just toss a round wooden seat on the top and call it a day. It's functional, for sure, but nowhere near as creative as Arthur Schmitt's Anice Stool, which is a 3D printed plastic core that lets you use whatever material you want for the seat.
Looking for a way to cool off in the scorching summer heat? Toss the stool's plastic core—which can be downloaded for free (sort of) from Thingiverse and 3D printed—in a bucket of water, place the whole thing in your freezer (if it'll fit), and in a couple of days you'll have a refreshing frozen seat.
Or if you're looking for something a bit more permanent, swap the water and freezer for some quick-setting concrete, and you'll have a stool for your patio that can withstand Mother Nature's worst. You could even bake it into a cake if you wanted to get really creative. Just make sure you blow the birthday candles out before taking a seat. [Arthur Schmitt via Notcot]