Open Tool Kit (Otk) is a portable widget library for making graphical user interfaces for C programs. It emphasizes simplicity for the application programmer without eliminating capability. Based on OpenGL, Otk supports Linux, Unix, and other OSs neutrally and efficiently. It is simple and compact, and it strives for easy compilation and linking to other applications. In seeking to address several issues associated with earlier graphics APIs, Otk explores some interesting methods, such as window-relative layout instead of pixel-based layout.
GTK, which stands for the Gimp ToolKit, is a library for creating graphical user interfaces. It is designed to be small and efficient, but still flexible enough to allow the programmer freedom in the interfaces created. GTK provides some unique features over standard widget libraries.
WebGUI is a content management framework built to allow average business users to build and maintain complex Web sites. It is modular, pluggable, and platform independent. It was designed to allow the people who create the content to manage it online, rather than content management taking up the time of busy IT staff. WebGUI comes with a full host of features including shopping cart, subscriptions, forums, photo galleries, FAQs, link lists, blogs, SQL reports, a Web services interface, and a very configurable user privilege and profiling system.
Zune is a free clone of the famous MUI (Magic User Interface) toolkit from the Amiga. It is primarily designed for C, and uses BOOPSI as an object-oriented layer. The MUI-apps developer should not care about "precise" graphic design (to let the user fully customize its application), and not care about resize (smart automatic layout algorithm). The MUI-apps user has maximum control over applications look and feel, and he can customize apps either globally or individually through a graphical prefs program.
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).
JSpell is a server-based spell checker that allows you to spell check any HTML input field and form. It is i18n compliant and has dialogs for multiple languages available. It can be used to add spell checking capabilities to HTML forms on your Web site. This spell checker is compatible with JSP, ASP, CGI, PHP, Cold Fusion, Oracle Forms, etc.
KaiView is a GUI toolkit/framework for writing applications using the TOM programming language. Based on a vector-oriented drawing layer using libart and freetype2, it provides a widget layer with subject/view separation, forms loaded from XML files, live updates to the GUI, Unicode support, abstract manipulator classes, antialiased everything, and a lot more.