Well, in my case specifically, it was a program that generated coloured images based on a set of simple rules (namely, don't reuse the same RGB colour for any pixel & try to be as close to the colour of neighbouring pixels as possible). I wrote a brief overview around the time I finished the first version[1].
More recently, I wrote a new routine which generates several of those and then averages the RGB channel values on a per-pixel basis, and then repeatedly re-averages the original images with those average images to create more "generations." I haven't written anything up about that because the code required to sum and average pixels in a PNG is significantly less interesting.
