Lost Levels, a site devoted to investigating unreleased games from distant memory, has presented some very interesting details on a Final Fantasy demo that was, at the time, assumed to be for the Nintendo 64. The demo predated both the console's release and Square's announcement they would take the series to the Sony PlayStation.
The demo was actually a reimagining of a battle from Final Fantasy III (Final Fantasy VI in Japan) and ran on SGI ONYX workstations, leading to many rumors that Final Fantasy VII was bound for the 64. The demo even sported some novel control styles; spells could be cast by drawing a star with the system's mouse, for example; could this have been a predecessor of some of the gesture-based control we've seen on the Nintendo DS?
Lots more details can be found in the Lost Levels article. Lost Levels only has a handful of articles, but they're all very interesting looks at gaming's past.