[X-Unix] X11 Gnome2 KDE ?

[Richard]

Just install Apples X11 app, and also Gimp 2.x
now I was looking to install another app, however, even though
it states for X11 windows there a requirement for gnome2....

excuse, the newbie, is this another x-window system, that I have to
install on top of apples X11 to make this app work?

enclose, there was another app, with the same setup X11 windows,
and then KDE requirement?

Thanks -
Rick