I am thankful that portableapps has Darktable, but it's missing digiKam which would be very helpful. Both programs are for photography but serve completely different goals. Darktable is more of an adobe Lightroom replacement for editing/composting, But digiKam is more of an adobe Bridge replacement for image management & tagging.
Darktable is basically focused on image manipulation with a barely passable image management function, and digiKam is mainly an image management program with a rudimentary image manipulation function. They really are two sides of the coin and having them both on a usb/portable drive would be *very* helpful when traveling.