This is one of my absolute favorites. It's so incredibly simple but I think that's what makes it look so cool.
Each line in the image is drawn with a random movement corresponding to the center of the circles. The default output vaguely resembles writing on a page.
See More: GitHub
Like many of the other pieces, there are several ways we can alter the results. Playing around the colors is obvious, but interesting things happen with other changes as well, such as line width, circle size, and movement restraints. Here's a few variations.