Circa Win95 - Win2000 windows always reminded me of NeXTSTEP windows, and I wonder if that's where Microsoft got it's inspiration.

Edit: Here's a mirror of a document that purports to be from a Windows 95 design team member: https://socket3.wordpress.com/2018/02/03/designing-windows-9...

Edit2: And a Hanselman podcast episode with Kent Sullivan and Derek Hoiem: https://hanselminutes.com/628/a-history-of-the-windows-95-st...