The freedesktop.org project provides a shared high-color desktop
icon theme shell for use under both KDE and GNOME desktops. This
is a glue port providing a symlink so that Linux apps find their
way around.
GNOME theme with FreeBSD colors
This is a GTK+ 2.x engine based on Bluecurve. It features a modern look
without sacrificing (much) speed.
microGUI for Metacity is a port of the Sawfish theme microGUI to Metacity.
The AquaFusion iconset for Gnome
The Crystal iconset for Gnome
The Widget Factory is a program designed to show a wide range of GTK+2
widgets in a single window.
Collection of Sawfish themes maintained by Debian
FlowCanvas is an interactive Gtkmm/Gnomecanvasmm widget for "boxes
and lines" environments (ie modular synths or interactive finite
state automata diagrams).
The Fast Light ToolKit ("FLTK", pronounced "fulltick") is a LGPL'd C++
graphical user interface for X11.
FLTK provides modern GUI functionality without the bloat and supports
3D graphics via OpenGL and its built-in GLUT emulation.
FLTK is designed to be small and modular enough to be statically linked,
but works fine as a shared library. FLTK also includes an excellent UI
builder called FLUID that can be used to create applications in minutes.
This port tracks the development snapshot releases of FLTK.