A hexagon cake knife is a knife that can cut cake into hexagonal pieces. Matthias Wandel, who is an engineer by trade but moonlights as a woodworking wizard (see his eminently watchable YouTube channel), was in need of such a knife, so he designed and crafted one himself.
I’m not kidding about Wandel’s YouTube channel; if you’re into this sort of thing, it is a Schedule-I time vortex. His recent creations include a Jenga pistol, a 60-sided geodesic dome, and, my personal favorite, a slinky machine:
Most of Wandel’s videos have a corresponding article on his website, which is also great. Explore at your schedule’s peril.
Contact the author at firstname.lastname@example.org.