I mean the ‘real’ one which was introduced in Windows 95 - up to Windows 8 (IIRC), which could be separated from the Taskbar and be docked at any side of the desktop, horizontally or vertically, and could also be stacked in both directions.
Let me dock/add-to-tabbed-pane/split-dock-into-multiple-panes and have the autohide/pin toggle for any window attached to any any edge of the screen, and make the Taskbar and the Quicklaunch and the Start Button just another set of Pane Windows, just with enforcement that (where appropriate) they cannot be closed or otherwise removed from the active screens, with a redundant always-accessible explorer rclick-context entry just in case you've somehow completely lost them.
Then make "maximize" mean "join the central pane as a new tab".
Yeah no. Enable full-width taskbar icons (like the Windows XP style wide ones) and notice how each one of them is of a different width. It's just terrible, it's almost like someone told an intern who's never used anything prior to Windows 7 to design it.
Why my rectangle window has round corners ? Where is the scrollbar ? /s