XmMol is a desktop tool designed to provide both interactive molecular graphics on X11 displays and easy interface with external applications. A kernel provides an interactive wire-frame display of macromolecules. It supports depth cueing, 3D clipping, and stereo. Various representations, coloring, and labeling modes are proposed. Docking and interactive backbone deformation tools are also supported. Communication protocols allow the user to develop new external features or to use XmMol as a visualization tool for external numerical programs.