The closest modern equivalent is the Keymouse Track and it's awesome. Source: 12 months ago

A somewhat more obscure, and fairly spendy option, is the KeyMouse. Each half has an optical sensor built into the bottom, and they also have trackball versions. Source: about 1 year ago

Well, there's the Keymouse which is a split keyboard with a mouse sensor under each half. That had quite a long development period - IIRC it was going to have smaller keys with Cherry ML low-profile switches so it wasn't too huge, and lots of people in here complained and asked for MX regardless of size. Source: over 1 year ago

I distinctly remember playing this on armorgames.com. You went around this house cleansing it (i think) of evil spirits. You could only see them if you wore some kind of mask. You knew where it was when you found a half eaten rat on the floor. I cannot for the life of me find it on the site anymore. I don't remember the name to even know if it still exists anymore. Source: over 2 years ago