Graphical user interface builder for Motif provides a visual reuse environment that speeds development of mission-critical applications.

Extend the power of ActiveX to all major enterprise operating systems. Includes add-on products, free download, and a developers' corner.

GUI toolkit for X11 is a C library built on top of Xlib and includes a set of 30 widgets and a 3D graphics library. Released under LGPL.

Cross-platform multimedia authoring and GUI development environment for Windows, UNIX, and Macintosh. Offers a free starter-kit download.