Originally released for use in the Linux desktop environment, GIMP has grown by leaps and bounds, becoming a very powerful, popular, and versatile program used by millions around the world.
GIMP is a graphics editor used to process digital graphics and photographs, and is very similar to Adobe Photoshop.
Typical uses include creating graphics and logos, resizing and cropping photos, altering colors, combining multiple images, removing unwanted image features, and converting between different image formats. GIMP can also be used to create basic animated images in GIF format.
GIMP's manipulation tools can be accessed via the toolbox, menu paths, and dialog boxes (which are also known as palettes). They include filters and brushes, as well as transformation, selection, layer and masking tools. GIMP comes with 48 standard brushes, plus facilities to create new ones. Brushes (and brush tools) can be used in hard-edged, soft-edged, or eraser modes, be applied at different opacities, or used with different modes for composition.
Don't spend hundreds of dollars on Photoshop, when GIMP will do it all for a fraction of the cost.