GIMP is the open source answer to Adobe Photoshop.  GIMP has much of the same functionality that Adobe Photoshop has, ranging from being used as a simple paint program, photo editing, an image renderer, or an image format converter. 

Being open source GIMP was built to except plug-ins and extensions that can be designed to do just about anything.  If you are looking to do any image editing and you can’t afford the price tag on most image editing software solutions GIMP provides you with the same features at no cost!

• Customizable Interface
• Photo Enhancement
• Digital Retouching
• Hardware Support
• Supported file formats: JPEG (JFIF), GIF, PNG, TIFF and special use formats such as multi-resolution and multi-color-depth Windows icon files .PEG(JFIF).
• Supported platforms: Microsoft Windows (XP and Vista)

GIMP is open source software and is made freely availble for personal use. Source code and license information for GIMP can be found at the GIMP Project Page.