GIMP is a cross-platform image editor
available for GNU/Linux, OS X, Windows
and more operating systems. It is free software.
Whether you are a graphic designer,
photographer, illustrator, or scientist, GIMP provides you with sophisticated
tools to get your job done. You can further enhance your productivity with GIMP
thanks to many customization options and 3rd party plugins.
Available for Windows, Mac OSX and Linux.
Please download at http://www.gimp.org/downloads/