From GNUstepWiki

Here there is a theme for your GNUstep Apps. Mainly this theme are for people that use desktops like Gnome, KDE, Xfce,... You can set the theme with

GNUstep SVN Themes

GnomeTheme is a plugin to make a GNUstep theme based on the active Gnome theme. Is under development.

The GnomeTheme has recently been renamed Gtk.theme since it really is a Gtk theme. It is available in GNUstep's SVN repository under the plugins directory. Check it out here:

WinUXTheme is the theme for Windows. You can active this on installation or with

Gap Themes

You find more at GAP.

Etoile Themes