It's a UI innovation that is found in OS X, but Apple did not invent it.
I meant my list to be more like: here are some big innovations in window-based GUI computing, which can be found in OS X. Not that these are all exclusive to OS X.
People say nothing has changed in desktop GUIs but I remember the dark times before tabs and window managers. Constant dragging, resizing, and minimizing windows just to keep track of things. Same with desktop search--constant careful folder curation just to keep files from getting lost and forgotten.