Freeglut is a free-software and open-source 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) takes care of all the system-specific chores
required for creating windows, initializing OpenGL contexts, and
handling input events, to allow for truely portable OpenGL programs.