Gospel Principles" because a free, offline one does not yet exist. For many reasons, I decided not to go through with it, but I found an alternative that may just be even better. The Dropbox app for iPhone allows you to select favorite files for offline viewing. This, of course, only works on files that are viewable by the iPhone (pdf, doc, ppt, xls, txt, etc.), but it does those very well. So I went ahead and just downloaded the pdf for each chapter in the manual, put them in a folder in my Dropbox on my computer, and then used the iPhone app to favorite the chapters I want to have available for offline viewing at church on Sunday.
There are really only a few downsides to this (but they are not outweighed by the task of writing an iPhone app). First, you have to download all of the chapters individually, which is about 50 files. Second, the file naming scheme that they have isn't ideal (GP_2010_Unit05_15_13_ThePriesthood__eng_.pdf) so I went through and renamed them (13_ThePriesthood.pdf). Third, you have to go through and favorite each individual pdf on your dropbox app. Fourth, the favorites view in the app only uses sections for the first letter of filenames and doesn't allow any sort of manual grouping, so if you have many other files in your favorites it can be hard to find what you are looking for.