The GIMP is the GNU Image Manipulation Program. It 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.
My friend, Felix Leong introduces me this great software, GIMP. It is an open source image editing software which works like Adobe Photoshop or CorelDraw. It can run on multiple platform: Unix, Windows and Mac OSX.
The software looks sophisticated and comes with advanced manipulation like full alpha channel support, layers and channels, multiple undo/redo (a very important feature), editable text layers, transformation tools and etc. Will give it a try and might become my default tools in future for creating images for my websites.
You can download the free software at the following link:
http://www.gimp.org/downloads/
Below are some of the screenshots of GIMP running different operating systems:
GIMP for Unix

GIMP for Linux

GIMP for Windows

GIMP for Mac OSX
