This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.
FreeGLUT is a free-software/open-source alternative to the OpenGL Utility Toolkit (GLUT) library.
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 trully portable OpenGL programs.
FreeGLUT is released under the X-Consortium license.