For practical info, I've used the Eorski app with good results.
Beyond the practical, into the prehistory and history of the road, I'd love also to recommend my own app, published by Sutro media and on iTunes and Android, The Esoteric Camino France & Spain (
http://www.beebesfeast.com/app-camino.html). After three decades of traversing the terrain, I noticed there were so many deeper layers to the Camino than we pilgrims often get to suss out as we pass. That inspired the writing--to point these out--and I also added in the folklore and local knowledge from the natives I spoke to who are guardians of the way.
Buen Camino!