XGui is a multiplatform, multilanguage native widget set. This means you can write your code once in your favorite language (C, C++, or Python) and then compile it to run on Linux or Windows with the native look of the OS. XGui is developed keeping in mind the MVC pattern. Lists and Trees are just views of a model. Even styles which define how to show the model in every different view are separated. GUIs, models, and styles can be saved and loaded from XML files.
The Ecere SDK is a cross-platform toolkit for building software applications. It currently runs on Windows, Linux, Mac OS X (through X11), FreeBSD, and the Android OS. It should run on other Unix platforms with minor testing/tweaking. With the Ecere SDK, you can develop applications once and deploy them on all supported platforms alongside a lightweight runtime environment. It introduces eC, an object oriented language derived from and fully compatible with C, compromising neither runtime performance nor ease of use. A built-in 3D engine supporting both Direct3D and OpenGL is fully integrated.
Wicket Web Beans (WWB) is an Apache Wicket component toolkit for displaying and editing POJOs that conform to the JavaBeans specification. Web pages are automatically generated based on bean properties and certain conventions. If necessary, the layout, editability, and actions of these pages can be customized on an exception basis. In other words, the toolkit normally does what you'd expect, but when it doesn't, you can override its behavior.
RCP Toolbox is a collections of valuable custom widgets and composites for SWT, JFace, and RCP applications. Currently, this includes Coolbuttons, Duallist, CoolSlider, ScrollingLabel, PropagateComposite, and more. An Eclipse RCP plugin and sample RCP applications are also offered.
Webwidgets is a framework for writing Web applications as if they were desktop applications. It employs the same programming paradigm as GTK, Qt, etc. with a tree of widgets with callbacks for events such as a button press. It encapsulates page loads, session data, form handling, etc. into widgets with their own state. Webwidgets is focused on code reuse, rapid prototyping, and separation between graphic design, interaction design, and application logic. It is implemented in Python and uses the Webware application server framework.
IT Mill Toolkit is a server-side RIA (Rich Internet Application) library that provides a versatile set of AJAX widgets for Java programmers. Applications are programmed in Java and executed server-side. At the client-side (i.e. in the browser), enhanced GWT widgets are used for presentation.