freeglut is a completely OpenSourced alternative to the OpenGL Utility Toolkit (GLUT) library. GLUT was originally written by Mark Kilgard to support the sample programs in the second edition OpenGL 'RedBook'.
Since then, GLUT has been used in a wide variety of practical applications because it is simple, widely available and highly portable.
GLUT (and hence freeglut) allows the user to create and manage windows containing OpenGL contexts on a wide range of platforms and also read the mouse, keyboard and joystick functions.
The freeglut project is released under the X-Consortium license.
The original GLUT library seems to have been abandoned with the most recent version (3.7) dating back to August 1998. Its license does not allow anyone to distribute modified library code.
This would be OK, if not for the fact that GLUT is getting old and really needs improvement. Also, GLUT's license is incompatible with some software distributions (e.g., XFree86).