1993: Apple Newton
The Newton is the quintessential before-its-time piece of technology: its utter commercial failure is undeniable, but its descendants are undeniably omnipresent.
The reasons for the Newton's flop are numerous: it was too big and too pricey, and its handwriting recognition software was spectacularly unreliable. The Newton's more successful imitators are equally numerous, and just about every PDA and smartphone can trace its lineage directly back to the Newton -- including Apple's iPhone, which, like most of its competitors, now accepts input from a keyboard, dispensing with handwriting recognition altogether. Curiously, Newton's handwriting-recognition technology was ultimately ported to Mac OS X, where it's known as "Inkwell." It hasn't really taken off there, either.