Here is an excerpt from their web site - ShiftN permits correction of converging lines; a majority of the correction work is taken over automatically by the program. Using the "automatic correction" item in the menu is in most cases sufficient to produce a satisfying result. Both the effects of converging lines and poor camera angle are corrected automatically.
It's a quick download and very cool to run on your images. If you have horizontal converging lines, try rotating your images, then run ShiftN for a very different result. Here is the ShiftN link for the whole story and download. Have fun.