GIMP

FROM WIKIPEDIA (its a wiki too)

GIMP (GNU Image Manipulation Program) is an image retouching and editing tool and is released under the GPLv3 license as free and open-source software. There are versions of GIMP tailored for most operating systems including Microsoft Windows, Mac OS X and Linux.

GIMP has tools used for image retouching and editing, free-form drawing, resizing, cropping, photo-montages, converting between different image formats, and more specialised tasks. Animated images such as GIF and MPEG files can be created using an animation plugin.

The developers and maintainers of GIMP have a product vision for GIMP to strive to be a high end free software graphics application for the editing and creation of original images, photos, icons, graphical elements of web pages and art for user interface elements