I think I haven't released this anywhere yet, so I'll put it up for download here. This is packPNM, my compression software for PNM (.pgm, .ppm, .pbm) image files. Two versions are included in the archive, v0.9 which is based on the algorithm used in packJPG <= v2.3, and v1.0d, which is based on the algorithm in packJPG >= v2.4. Although I had hoped v1.0d to be better in each and every case, v0.9 is still better for some images.
This is more or less an experiment wether the packJPG algorithm could be reused for different, non DCT based image types as well. The results might not be that fantastic for grayscale (.pgm) or RGB (.ppm) images, but the compression algorithm for mono (.pbm) images is quite good and very simple as well.
I'd open-source this as well, but the source code right now is a mess. I wouldn't release it the way it is now, so that would need work, too. If there is interest for the source code, I'd see what I can do.