GIMP is the GNU Image Manipulation Program. It is an open source software design for photo retouching, image composition and image authoring. The main features of Gimp are:
- layers and channels
- painting tools: brush, pencil, eraser, airbrush
- custom painting tools can be imported
- transformation tools: rotate, shear, flip and scale
- selection tools: rectangle, ellipse, free, fuzzy
- undo / redo
- alpha support
- animation support
- many file formats supported: bmp, png, jpeg, gif, svg, psd, ...
- and many more features...
Gimp can also be extended using plug-ins. More than 100 are registered on the Gimp Plugin Registry site.
Warning: current Gimp version is only compatible with Windows XP SP2 or newer version (Vista, 7).

Windows
Linux
MacOSX