smart phone on the PCT

This summer I spent a day walking with a gentleman from Germany who was using a Sony smart phone with an app on the PCT and a downloaded National Geo map. By using the airplane mode he was able to follow the trail with very specific info on water sources, camping spots, etc. He had a small solar charger  which worked great for him. I've misplaced his e-mail and I wonder if anyone can give me links to the app (s)? I thought his method was superior to the "pieces of the guidebook" method I employed or the PCTA guides folks were carrying. 

Thanks,

Bruce