GIMP Paint Studio is a creative commons set of tool presets,
brush presets, color swatches, patterns, and config files that will
transform the GNU Image Manipulation Program into a robust painting and
materials-emulation application.  Great for painters, airbrushing and
re-touching, and illustrators.

Note that this will overwrite any config files you might already have
in /usr/share/gimp/2.0 although it does back the old ones up just in case.