XView (X Window-System-based Visual/Integrated Environment for Workstations) is a user-interface toolkit to support interactive, graphics-based applications running under the X Window System. XView provides a set of pre-built, user-interface objects such as canvases, scrollbars, menus, and control panels. The appearance and functionality of these objects follow the OPEN LOOK Graphical User Interface (GUI) specification. XView features an object-oriented style Application Programmer's Interface (API) that is straightforward and easy to learn.
SMOOTH is an object oriented windowing toolkit written in C++. It is meant to become an alternative to toolkits like Qt. SMOOTH provides classes for windowing, session management, object distribution, and multithreading. It currently only works under Win32, but a Linux port is being actively developed.
picoTK is a C GUI toolkit that requires only a minimum of memory resources. It is intended for embedded system use, especially for (but not limited to) the RTEMS realtime kernel. It is in no way comparable featurewise to a "real" full blown windows toolkit like Qt or nanoX; it rather provides simple drawing primitives like lines, filled rectangles, characters, and pixmaps. (But that is what many embedded applications might ask for.) It directly works on tailored "framebuffer" hardware. A Linux framebuffer emulator is supplied as part of the kit, making evaluation (and emulation!) possible without having a realtime OS and custom hardware.
OIO is a Web-based metadata/data management front-end which is built using Zope and works with Postgresql. No programming is required to build and manage Web-forms or to perform data mining/analysis on the collected data. It is in production at the Harbor/UCLA Medical Center for clinical outcomes management and research data. Forms created with OIO and hosted on any OIO server can be downloaded as XML files. Once downloaded from the "Forms library" and imported into an OIO server, the necessary database tables are automatically recreated and the imported forms become immediately available to the users of that OIO server.
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.
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.