SDLTk is a generic widget library that uses images as widgets. It supports a large number of widgets and customizations.
TouchWidgets is a widget library for touch-based Linux devices using X Windows. It has support for animations and momentum-based scrolling.
(commercial) a User Interface Management System (UIMS). It enables software developers to create user interfaces with OSF/Motif widgets
wxAdvTable is a table widget (like wxGrid) designed with simplicity and flexibility in mind. It has many advanced features like: - composite rows/columns - sorting and filtering support - flexible rendering and editing support - dynamic row/columns add/removal - visual features like: highlight modes, cell attributes, etc.
wxHarbour is a set of [x]Harbour language bindings for wxWidgets, providing a portable GUI toolkit for [x]Harbour.
generates new wxwidgets projects, with a main frame and text or drawing/imaging window, provides a simple code editor, generates makefiles and calls the compiler for wxwidgets projects
Xaw-Xpm makes numerous aesthetic improvements, as well as the ability to put colour
background pixmaps (images) into almost every widget.
a group of three Motif-based widgets, originally part of the Bellcore Application Environment.
Xew contains a set of widgets for displaying and presenting the basic information types, such as text, images, graphics, audio and video.
a group of larger and smaller utility widgets, authored by Rick Scott
Zero Memory Widget
The Zero Memory Widget library is as powerful as classic widget libraries, but it does not use a single bit of memory per widget. So with this library, there is no widget pointer/reference, instance creation/destruction, event handler function, functions to read/write data between widget and application, and so on.