GIMP2.8 Script-Fu is a collection of over 100-scripts free and available for download. Vrious pencil strokes, contrast, edges, effects (bevel selection, etc) shapes, etc are available in Script-Fu.
here is how to get Script-Fu installed on a Debian box.
1) download the Script-Fu bundle from here: http://www.gimphelp.org/script28.html#downloads
2) Launch GIMP, go to Edit Menu >> Preferences >> pull down Folders >> Scripts
by default, there are 2-folder paths there:
3) Copy the downloaded file: mine was a .zip, I extracted it into a directory under 'scripts'. Use the folder icon in the figure above to locate the extracted script-directory.
4) From GIMP menu, to to Filters >> Script Fu and click "Refresh scripts"
Now you'll have an additional Menu-Item "Script-Fu"(with a host of sub-items) besides the 'Filters' menu-item
thats all folks...