One of the best free graphic design programs GIMP is a GNU Image Manipulation Program. This software helps for photo retouching, image composition, image authoring etc.
It works on multiple operating systems and in multiple languages. It is cross-platform graphic design program which is available for all linux, mac & windows. It provides all the sophisticated tools for all graphic designer, illustrator, photographer or scientist. There are certain third party plugins are available which can helps to increase your productivity. This all features of the GIMP makes it one of the best and most installed graphic designing software.