Xsquig displays squiggley tubular patterns in the root window. Sample snapshot:
The original version of this program was Sun-specific, and wrote directly to the screen. It ran at a respectable speed on a SPARCstation 1. This version, going through all the layers of X and having to move about a hundred times more pixels because X can't efficiently draw a list of points of different colors, is too slow even on a SPARCstation 10. Maybe next year. Meanwhile, if you have a Sun and want to see how fast the original version runs, fetch raster-pixrect and build "squig".