Xclasses is a C layout library for the X Window System. All objects (called gadgets) are font sensitive, i.e. their size changes with the size of the used screen font and the size of the window. All this is done by Xclasses itself. The user may choose any kind of font style and size.
Kiwi is an object-oriented framework for developing graphical applications using Python. It has a set of classes that provide a solid application architecture, and a set of high level graphical components that can be used as drop-in replacements for some of the widgets in PyGTK, including CList, CTree, Label, OptionMenu, and more. It includes a complete developer's manual, with examples and screenshots, and full API documentation.
XWidglets is a complete rich Java Swing tool for designing, creating, and using XML-based GUIs. It provides a lightweight XML client, clear separation between view, data, and process, MVC I and II support, event management, a consistent look and feel across platforms, a rich set of GUI components, and n-tier architecture integration.
SDPGTK wraps GTK using simple, clean C++ classes and a straightforward hierarchy. It integrates well with existing GTK code, and, unlike existing wrappers for GTK, does not force the developer into a UI "framework". Of particular interest is the sdpGtkObjectContainer class, which implements the proposed GTKML standard, for loading a GTK hierarchy and events from an XML document.