The GIMP is designed to provide an intuitive graphical interface to a
variety of image editing operations. Here is a list of the GIMP's
major features:

 Image editing
 -------------

   *  Selection tools including rectangle, ellipse, free, fuzzy, bezier
      and intelligent.
   *  Transformation tools including rotate, scale, shear and flip.
   *  Painting tools including bucket, brush, airbrush, clone, convolve,
      blend and text.
   *  Effects filters (such as blur, edge detect).
   *  Channel & color operations (such as add, composite, decompose).
   *  Plug-ins which allow for the easy addition of new file formats and
      new effect filters.
   *  Multiple undo/redo.

WWW: https://www.gimp.org/