> windows should be square
found the Windows 8 enthusiast! haha, I kid. (I myself use a tiling window manager , i3, with completely square windows without any gaps or rounding)
My custom XFWM theme has square corners on windows without focus and large-radius rounded corners on the one window with focus.
The square corners are part of a 2 pixel wide border (one black, one white) because who needs to waste space on handling things we aren't manipulating? But the title bar is high-contrast, because you'll go looking for it when you want to switch windows.
The round corners go with a fairly thick border in a customizable color, usually something very bright in the yellow, orange or cyan ranges. When you sit down, you should immediately know what is active.
I like rounding the corners on i3. It is a bit wasteful but the base WM is so efficient with my pixels that I have some to spare.
Not having i3 is truly the worst part about Macs.
(Yes, please tell me about some buggy half-compatible tiling window manager for my Mac.)
Haha, Windows had square windows long before 8.
If I could run the Windows 2000 UI on a modern OS I would but any recent clone/theme/etc feels too uncanny valley.