More on the Open Apple/Closed Apple saga from Joe Strout:
Both the Open Apple and the Closed Apple were actually paddle buttons, malady and typically were used only for games — situated to the left and right of the scrollbar, they were perfect for things like pinball. Open-Apple did not have any meaning as a modifier key until Appleworks (the original one, not ClarisWorks which came much later) started using it that way, and even then, it was just the convention of that program, not a platform standard.