I'm fairly sure it's never been called Aqua; "Aqua" is the name of the standard UI look (cf. the NSAppearance class). But the window manager is Quartz: "Quartz

I'm fairly sure it's never been called Aqua; "Aqua" is the name of the standard UI look (cf. the NSAppearance class). But the window manager is Quartz: "Quartz Compositor is the display server (and at the same time the compositing window manager) in OS X." https://en.wikipedia.org/wiki/Quartz_Compositor https://en.wikipedia.org/wiki/Quartz_Compositor (Hence the name "XQuartz" for the X11 display server.)