It's a small cube, about one inch on each side, that has various knobs, switches and buttons. It's similar to a stress ball that you squeeze but allows you to 'fidget' with your fingers. I find myself randomly grabbing it while working and playing with the different knobs, switches, and buttons. More often than not it's the switch that grabs the attention of my fingers. It's a nice option to keep my hands active while thinking through what to write next or when I'm talking on the phone when sitting at my desk.
These little guys are relatively cheap too. A quick search on Amazon shows you can purchase one for just a couple of dollars. Now I just have to see how long it takes before I wear out the switch!