DiaCanvas is a generalized version of the drawing canvas used by DIA. It extends some features used by DIA and adds new ones, while preserving as many of the original features as possible. This project is no longer actively maintained. It is suggested that you try DiaCanvas2 instead.
FOX is a C++-based toolkit for GUI development. It includes a rich set of widgets and has powerful yet simple layout managers, MDI widgets, and mega-widgets. FOX incorporates support for XDND for drag and drop, X clipboard and X Selection, watching other I/O channels and sockets, timers and idle processing, object serialization and deserialization, a registry to save persistent settings, and 3D widgets using Mesa or OpenGL. FOX works on Linux, IRIX, Solaris, HP/UX, AIX, Tru64 Unix, Windows 9x,NT,2K (VC++, GNUWIN32, Borland, VisualAge C++), FreeBSD, and Sequent.
gtkmm (previously known as Gtk--) is a C++ interface for the popular GUI library GTK+. It provides a convenient interface for C++ programmers to create graphical user interfaces with GTK+'s framework. Highlights include typesafe callbacks, widgets which are extensible by inheritance, and many classes that can be easily combined to quickly create complex user interfaces.
GtkCanvas is a straight port of the GNOME Canvas from the stable gnome-libs 1.2.4 back to gtk+. This widget behaves identically to the GnomeCanvas widget, with the same APIs, except the names are changed from gnome_canvas to gtk_canvas. Since the next version of gtk+ will drop GdkImLib and intgrate with gdk-pixbuf, it is expected that future versions of this widget will depend upon gtk+ only. It is intended that GtkCanvas will follow GnomeCanvas closely, merging new code whenever a stable release of the latter is made. Thus this is not really a fork but rather a "re-packaging" of the same code.
GtkDatabox is a widget for the GTK+ library designed to display large amounts of numerical data quickly and easily. It allows for one or more data sets of thousands of data points (X and Y coordinates) to be displayed and updated in split seconds. It offers the ability to zoom into and out of the data, and to navigate through your data by scrolling. In addition to rulers and a simple coordinate cross, it allows you to add one (or even more) configurable grids like on an oscilloscope. Data may be presented as dots, lines connecting the data, or vertical bars. The widget allows you to easily transform pixel coordinates into data coordinates, thus allowing you to easily create powerful applications for data analysis.
GTKExtra is a useful set of widgets for creating GUIs for the X Window System using GTK+. It is written in C and includes the following widgets: GtkSheet, GtkPlot, GtkPlotCanvas, GtkItemEntry, GtkComboBox, GtkColorCombo, GtkBorderCombo, GtkFontCombo, GtkDirTree, GtkIconList, GtkFileList, GtkIconFileSelection, and GtkCheckItem.
Libsx -- the Simple X library -- is a lightweight wrapper library sitting on top of the Athena Widget set, as implemented in Xaw and variants (Xaw95 yields much nicer results than Xaw in comination with libsx). Libsx does not compete with GTK or Qt, but nevertheless allows you to write a lot of small (or bigger) programs painlessly, with no or little knowledge of X programming. With libsx, writing a simple program that opens a window, has a few buttons, and draws some graphics (lines, circles, bitmaps, etc.) is a matter of 5-10 lines of code, including the drawing code. Hello World is 2 lines. More complicated programs that respond to mouse clicks, have buttons, scrollbars, file browsers, a color selector, etc., can be written in 25-50 lines of code.