Toroflux®

I keep this on my desk and it's genuinely hard to put down once you start rolling it between your hands. The metal has a nice weight and the rings glide smoothly, though it took me a few days to get the flick motion right.

The way the five rings pop open into that 3D shape when you tap the stack is genuinely hypnotic. My only gripe is that the metal gets a little noisy after a while, so I save it for short desk breaks rather than long stretches.