a high-level multi-platform, thread-safe C/C++ windowing and graphics library built upon a fast, low-level graphics kernel. (new feature is FGX - dynamic GUI via XML file aka XUI file format)
a free user interface builder for GTK+ and GNOME interfaces designed are saved as XML, and by using the libglade library these can be loaded by applications dynamically as needed. (Glade can also generate C code)
port of the X Window System server to Windows. It shares the same source code base as Cygwin/X, but does not depend on the Cygwin environment or cygwin1.dll. Xming is a fully featured X11 server for Windows that is very simple to install and use.
is a layer above the existing toolkits available (Win32 API, GTK, Cocoa, ...). The result is that applications look and function like the user expects on their respective system. Mozilla Public License
a 2D graphics library, support for multiple output devices. (output targets include the X Window System, Win32, image buffers, PostScript, PDF, and SVG file output. Experimental backends OpenGL (through glitz), Quartz, and XCB.