Thinking of small form factor devices, I wanted to mention that at one point in time I was a heavy Rex 6000 user.  To me this was a great extension of first my laptop and then my first tablet.  It would sit in my PC Card slot and whenever I went away to a location where taking my laptop or tablet wasn't what I wanted (e.g. dinner) it made the best PDA I ever had since I could easily put it into my pocket and pull it out for that quick data entry.

I found mine the other day in a heap of old technology at home while cleaning up, and figured that maybe I'll start using it again.  Went to the ratshack to get batteries and found the old software, but alas for some reason or another it just doesn't want to install on my latest laptop.  No clue why it doesn't install -- I don't get any error messages along the way and the install program happily goes about it's business but when it's finished, there's no software installed anywhere, just an empty folder in program files.  The wonders of software....