Changes thickness of lines in line art. Enlarges visible image, repeatedly blurs, thresholds, and antialiases, then shrinks image down to original size. A dialog prompts for amount of enlargment, number of repeats, speed of line thickness change, and whether to make the line thicker or thinner. As of v. 1.5 the result is put into a new layer, leaving the old image untouched.
The color tools (Levels, Curves, Threshold...) memorize all settings used. Over time these accumulate, slowing down tool startup, and making it more difficult to reach the explicitly saved settings, which appear at the bottom of the list.
The settings-cleaner script will run automatically at each Gimp startup and do some housekeeping on these files, directed by a short configuration file, keeping at most a specified number of settings not older than a specified number of days. Settings that have been explicitly saved with a name are of course left in.