I've always had a major soft spot for the Halfkeyboard, even if its actual implementation was kind of a disappointment (too light, too laptop-keyboard-like, and some of the outer keys just weren't quite "right" due to the need to make a perfect rectangle instead of having a more "ragged" perimeter with oddly-shaped modifier keys that were easier to hit with less gymnastics).
I've ALWAYS thought it was something Microsoft should have licensed from him & made a standard part of Windows (at the driver level).
Deficiencies aside, my halfkeyboard is a gift from ${deity} for CAD work, because it lets me work with one hand on the keyboard, and my other hand on the mouse. I don't use it a lot for "general-purpose" typing, but I couldn't live without it when I'm laying out circuit boards and have to constantly enter one-letter commands, or type label names & numeric values.
Someday, when I have a few months to spare, I'm going to take an Arduino Leonardo & build myself a PS2 to USB adapter that implements inline halfkeyboard logic, so I can have "always available" halfkeyboard functionality with my Model M13... after I get around to implementing a two-button Morse'ish input method for blindly typing with one hand while driving ;-)