The Apple Newton would have been absolutely mind boggling if it existed in 1990. Even as revealed in 1992 (and released in 1993) it was still quite the technological marvel in many respects.

Its ultimate problem was that it was still ultimately more like a TI-83 graphing calculator than an iPhone. Much as people mocked the handwriting recognition, it was technology which could have been iterated upon. It turns out the key missing ingredient for the Newton was wireless internet access — and of course an internet worth connecting to.