GIMP is the GNU Image Manipulation Program is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages (77).

Version 2.4 of the GNU Image Manipulation Program is now available.

The release note contains the list of new features and some nice screenshots. You can download this semi professional tool at no charge

GIMP  run on any NT-based version of Windows (NT4, 2000, XP or Vista download HERE), and also on Macintosh  (download HERE)
Windows binary can be grab here while linux version are available at the main site

Some useful links to finish this small blog post GIMP Documentation