The G'MIC plug-in for GIMP proposes a set of various filters to apply on your images, including artistic effects, image denoising and enhancement algorithms, 3D renderers, etc.. It is a quite large plug-in, integrating a lot of different effects.
This script is nother in a series of planet makers. This one makes a banded gas giant. There can be anywhere from one to 20 bands in the planet. Each band is an equal height, and has Plasma noise rendered in it. Each layer is then motion blurred. The result is then mapped onto a sphere, and gaussian blurred to make the edges nice and fuzzy.