I remember RiscOS/Archimedes on the 90s Acorn computer had a great feature - the third mouse button, when used to click an item in one of the toolbar menus, would cause the command/item to execute but keep the menu up after the mouse click. So you could pick another item without navigating to the same menu again.

I've got no idea why this hasn't been ripped off or licensed. The only similar feature I've seen is Windows 7 letting you close windows from the task bar while keeping the window list open.