Dancing T-handle in zero-g
The intermediate axis theorem states that an object can rotate around its longest axis or its shortest axis without trouble, but stable rotation around its intermediate axis will be impossible. It's hard to observe this on Earth, but Dr. Ben Longmier asked an ISS astronaut to try this for YouTube. Now it's the first post on !physicsgifs@lemm.ee ! It only took 19 months.
There's a video game called besiege that lets you build things and test them against physics. I saw this gif and decided to test this effect by making this shape and spinning it with the gravity off. Sure enough it worked.
Whoa, what? Beseige, eh? It's game that lets you simulate things in a zero gravity sandbox? That's going on my wishlist really quick. Thank you!
Edit: IndieGala has the Steam version of Beseige for $2.24 this week in certain countries, including mine! Shout outs to IsThereAnyDeal for that.