Picturenaut combines multiple images into one. If you have exposed several photos of the same subject, each photo with a different exposure value (exposing for the darks in one, the mids in another, the highs in yet another), the combined image created by Picturenaut will select the best parts of each photo, resulting in an image with MUCH higher dynamic range than normally possible with digital OR film.
If you take the various exposures "by hand", that is: without a tripod, make sure you click the align images checkbox. Probably a good thing to leave that checked even if you do use a tripod.
There are a lot of options in Picturenaut that bear some experimentation, too.