Window manager themes.
RISC styled WM theme for Xfce4: http://www.marutan.net/themes.php.
GTK themes.
Mac OS Classic theme for Xfce4: http://xfce-look.org/content/show.php?content=144719.
Mac OS classic GTK2 theme: http://gnome-look.org/content/show.php/Mac+OS+9+Platinum+gtk+theme?content=110444.
Plane GTK: http://gnome-look.org/content/show.php/Plane-Gtk3.6?content=156309.
Classic 95 Windows `95 theme for MATE and Gnome: http://gnome-look.org/content/show.php/Classic95?content=157298.
How to create a look-alike Windows XP desktop using IceWM: http://kmandla.wordpress.com/projects/lookalike-windows-xp-classic/.
Windows 3.1 theme for Xfce4: http://xfce-look.org/content/show.php/Redmond3+%28Windows+3.1+theme%29?content=121526.
Windows 8.1 GTK theme for MATE and Gnome: http://gnome-look.org/content/show.php/?content=163556.
RiscOS GTK theme: http://gnome-look.org/content/show.php/?content=128771.
Fitts Metacity theme: http://gnome-look.org/content/show.php/Fitts?content=139285.
Wallpapers.
Comet landing wallpaper courtesy of the New York Times: http://thenypost.files.wordpress.com/2014/08/comet2.jpg.
Another awesome shot of the comet that the spacecraft has landed on: http://www.wired.com/wp-content/uploads/2014/11/Comet_on_19_September_2014_NavCam.jpg.
