EDIT: Just barely mentioned is Axiotron's ModBook --- while not a clone per se (a Mac Laptop was disassembled, keyboard removed, and screen either replaced or reinstalled w/ a digitizer layer), it was a device marketed to folks whom Apple did not have a product for, and until the Apple Pencil, was the best Apple device in between the Newton MessagePad or a Wacom Cintiq for stylus usage.
Wow, I thought I had been a big Mac, er, addict as a kid and somehow I never heard of these except maybe the Modbook.