The example programs for these notes use "GLUT", a utility toolkit created by Mark Kilgard  and contributed to widely by the graphics community.
GLUT is easy to use and simple, so it may appeal to beginning OpenGL users. OpenGL users of all experience levels can use GLUT to rapidly prototype an algorithm using OpenGL and not spend time writing the code to configure an X Window, setting up a Win32 color map, etc.
The GLUT library provides a number of convenience functions for handling window systems and input devices. Applications can request an OpenGL visual using a set of attributes and manipulate the window that provides that visual through a window-system-independent API.
GLUT provides pop-up menu support and device handling support for a variety of devices such as keyboard, mouse, and trackball, and invokes user-supplied callbacks to handle window events such as exposure and resizing.
GLUT also offers utility routines for drawing several geometric shapes as solids or wireframe models, including spheres, tori, and teapots.
Text rendering is also simplified by GLUT. Several bitmap and stroke fonts are provided with the GLUT distribution.
GLUT is available on most UNIX platforms, MacOS, and Windows NT/95, and other operating systems. It can be downloaded from http://www.opengl.org/Developers/Documentation/glut.html.