Yet another thanks to add to the pile for testing this one. I loved the transparency tool in this program.
Personal story ahead that doesn't really have anything to do with the photo editor or portability ...
My relationship with this program in part created my interested in portable freeware. As mentioned above, the transparency tool in this program was (probably still is) fantastic and I was using it in web development applications constantly. Then Microsoft pulled it out of their photo application and replaced it with a photo manager. I spent a LOT of time trying to find a program that would mimic this functionality and never really succeeded (GIMP comes the closest).
This whole thing happened again when Microsoft Photo Manager, got pulled from the latest version of Office. Again, that program's one great feature (a great thumbnail batch editor), was just irreplacable. A lot of posts here on the site come from an effort to find that (the closest I came was digiKam: viewtopic.php?p=65735#p65735)
It is of course possible to get both programs by jumping through some hoops, but it was a case of Microsoft deciding what is and is not important.