Here, we mention websites dealing with software projects or similar sites used as frameworks for GIMP or in its construction.
www.gnu.org is the official site of the GNU project. The GNU project is the oldest free software project in the world, and, in fact, this project founded the concept of free software. Initiated in 1983 by Richard M. Stallman, who desired a Unix-like operating system without any constraint regarding its freedom of use, change, and distribution, the project began by building all the necessary components but the kernel. This last has since been supplied by the Linux kernel. The intended GNU kernel, called Hurd, is still in alpha state. Remember that GIMP is an acronym for GNU Image Manipulation Program.
www.gtk.org is the official site of the GTK+ project. This software was initially the GIMP Toolkit, the widget toolkit used in implementing GIMP. Since its beginning, it has developed to the point of being one of the most important toolkits in GNU/Linux. For example, it is the basis of the GNOME desktop environment and is now object oriented (hence the name GTK+), and it has been ported to other operating systems like Windows and Mac OS X.
www.gimp.org/about/COPYING is the GNU General Public License (GPL), the most widely used license in the world of free software. A software product licensed using the GPL offers the four fundamental freedoms: freedom to run the program for any purpose, freedom to study how the program works and adapt it to your own needs, freedom to redistribute copies so you can help your neighbor, and freedom to improve the program and release your improvements to the public so the whole community benefits. Importantly, these freedoms cannot be denied by somebody redistributing the program.
www.gegl.org is the official site of the Generic Graphic Library, a graph-based image-processing framework. In the current version of GIMP, images are represented as arrays of pixels. When you edit an image, you change the pixels, and there is no way to return to the unchanged image other than opening a previously saved copy: This is called destructive editing. With GEGL, images are represented as graphs, in which the edges are image components and nodes are operations on these components. By changing the structure of the graph, you can perform nondestructive editing. Moreover, this representation offers provisions for representing images in higher bit depth than the current 8 bits. GEGL operations are already usable in GIMP 2.8, but only GIMP 2.10 or 3.0 will fully benefit from the incorporation of GEGL.