Earlier quoted context omitted.
Good point - though I believe they were called windows on previous GUI systems. EDIT: Though now that I think about it and, IIRC, Xerox's stuff didn't have overlapping windows either. Apple's Lisa and Mac did. I think Englebart's demo had windows but I'm not sure if they overlapped.
I recall a story (maybe an urban myth) about Steve Jobs visiting Xerox's labs and seeing their UI in action and thinking "we've got to have that". He went back to tell Woz all about it, telling him that Xerox's UI supported overlapping windows and that Apple needed to do the same. Woz was amazed that it was possible to have overlapping windows on such a resource constrained machine. But if Xerox engineers could do it…
According to the Apple stories I've read, Wozniak had little to no involvement with the creation of Macintosh. He was in a plane crash in 1981. When he came back to the company in 1983 he was mostly involved with the (increasingly sidelined) Apple II team.
But overlapping windows first came to Apple with the Lisa, anyhow. Some of Bill Atkinson's photos here show them from December 1979 or early 1980. Story says Bill wasn't sure whether they predated Apple's Xerox visit, or not. http://www.folklore.org/StoryView.py?story=Busy_Being_Born.t...
Anyhow, it's a good story. If it has some basis in truth it might be with s/Woz/Atkinson/ (he was their UI/graphics guru programmer) and s/Macintosh/Lisa/. :)