That's the officially deprecated for decades "Multiple Document Interface". Any app still using it will render that on modern versions of Windows.
The open source Windows all I maintain still uses this paradigm, and there's not really a good migration path to anything else, and Microsoft refuses to fix the chrome.
That's excellent. I wonder how deeply the UI elements go. Like can I produce a UI from Windows 3 or 2000 on Windows 11 if I make the right Win32 calls? Is the classic theme really gone, or just aggressively hidden? The new Windows 11 taskbar is definitely new code and doesn't behave like the old one, so I imagine you can't have a true classic taskbar on 11.
Yes, it's Windows Aero minus most of the 3D accelerated special effects. It was also used on low performance systems or if you RDP'd in to save bandwidth.
