Apple's Knowledge Navigator a better predecessor to Cortana
While Bob was certainly worthy of Microsoft's efforts, it's worth it to remember that MS was pretty much *always* playing catch-up to Apple in earlier parts of the 90's. System 7 was quite an advancement over Windows 3.1 and most of MS's user interface designs were not especially sound.
As far as Cortana goes, well it's clearly somewhat inspired by Siri. Siri, however, actually uses some legacy recognition technologies that harken all the way back to John Scully's Newton days. It was right around this era, when "personal digital assistance" were still 8-9 years off, that Apple produced its "Knowledge Navigator" video - a blue sky demo of what they thought human/computer action would be like in the future.
We're not quite there yet, and it's clear that no one had envisioned quite the degree of interconnected multitasking (aka, *completely* pervasive Internet) that we have now, but quite a fascinating watch.
https://en.wikipedia.org/wiki/Knowledge_Navigator
https://www.youtube.com/watch?v=-jiBLQyUi38