Lately I've been wanting a VR tool that does interactive 3D projections of 4D geometry. It's already so counterintuitive, I'm curious if the additional information available when projecting to 3D rather than 2D would allow better intuition for 4D transforms, volume-as-surface, etc. For some reason 4D geometry has always been an annoying obsession for me, like an itch that I can't scratch.