Otk is a portable widget library for making graphical user interfaces for application programs. It emphasizes simplicity without eliminating capability. It is based on OpenGL and C. Otk provides the following basic widgets: * Panel - The "container" widget, * Text Label - Text labels, * Button - Buttons with labels and call-backs to user functions, * Text Form Box - Accept text with function call-back, also scrollable editor window, * Pull-down Menu - Display hierarchical menu-lists with user function call-backs on mouse release, * Slider Control - Slider control with call-back, * Sub-windows - Detachable self-managed windows, * Gadgets - High level widgets