Holy fucking crap. g-lick-balls is not only one of the sweetest and most obviously right little compression algorithms ever, with the best acronym, it also has the absolute coolest source code . The original web page and PDF are gone from the net now, but fortunately these pieces remain. The hint text that went with the source code also contains some tidbits that weren't in the PDF article.
One of the other major lossless image compression algorithms is RkIm, part of the Rkive suite by my old compadre Malcolm Taylor. Malcolm was always a bit of a troubled weird character, and he seems to have disappeared off the face of the earth. His page is gone and I can't find any information about him or his work around on the net any more. Malcolm made the original Rkive right around the same time I wrote the original PPMZ; we were working in very similar territory, we had the top two text compressors in the world for a long time, he helped me work out many of the details of PPMZ and he made the best implementation of it. He was just a hobbyist, not employed, and I invited him to come out to Wild Tangent to interview when I worked there. He came out and was kind of weird, and then disappeared; he never replied to any followup emails or calls. I wonder what's become of him.