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.
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