citating http://www.maximumcompression.com/guestbook/gb.php :
go to http://compression.ca/act/act-jpeg.html
May 7, 2007
Hello everyone, I'm not dead just been very busy with family life and school. Not long after the last update in 2005, our first child was born, followed by me finishing my Masters degree, followed by me starting a PhD, and just last month our second child was born. I had a few minutes to add another JPEG compressor from Germany, this one is a pre-public version of packJPG written by Matthias Stirner. PackJPG so far gives the best JPEG lossless re-compression for a non-commercial application. Stuffit's new JPG compression still beats it, but you will soon have an open source alternative. I am told packJPG will eventually be released as open source and will be available for Linux and Windows along with a GUI. You can see the latest results here.