Gamma is a dynamically-typed, object-oriented, interpreted programming language that has been designed and optimized to reduce the time required for building applications. It supports the QNX/Photon and Linux/GTK GUI environments, and has a built-in library of over 300 functions. It cuts development times and offers run-time debugging by wedding a C-like syntax to a Lisp interpreter that has been optimized specifically for performance and memory usage.
The Xmt Library provides nine custom widgets and over 260 convenience functions designed to make Motif user interface development easier for beginning and advanced programmers. It provides an alternative tool chain that avoids the use of GUI builders. The essence of this approach is to program from the resources file using an extended vocabulary for automatic creation of the widget hierarchy, dynamic layout, and to provide a rapid prototype environment.
ClassyTk is an extension of Tk based on the ClassyTcl Object system. It adds a lot of improvements to Tk, ranging from drag and drop support (between Tk apps) and a configuration system to a large set of new widgets and commands, written using the object system. It also contains a GUI Builder that can be used to graphically create interfaces. It is invoked via the cbuild command in the bin directory. There are also some sample (but useable) applications created with ClassyTk: a very useable editor, a calculator, a drawing program, and more.
The JOpenChart library and toolkit provides the means to create different kinds of charts, including pie charts, line charts, and plot charts. Furthermore, it contains components for embedding charts into Swing or Web applications. The library's Renderer Interface API makes it very easy to add new renderers for different chart types. Classes to interpolate measured data and to plot mathematical functions are also included.
Tkinter is Python's de facto standard GUI (Graphical User Interface) package. It is a thin object-oriented layer on top of Tcl/Tk. To use Tkinter, you don't need to write Tcl code, but you will need to consult the Tk documentation and occasionally the Tcl documentation (since Tk's low-level event handling mechanism is considered part of Tcl).
Luxor is an open-source XML User Interface Language (XUL) toolkit in Java that lets you build UIs using XML and also includes an ultra light-weight, multi-threaded Web server, a portal engine, and a template engine. It is also Web Start-ready, as everything fits in a jar and requires no loose files.