FarOut (Formerly Guthook) is one of the most popular apps used by Thru-Hikers, Section Hikers, and Long Distance Backpackers.
The app is free with certain maps that can be purchased for download. Each map, for example the Appalachian Trail, will have waypoints listed along the route including water sources, campsites, vistas, and more.
Once the app is setup it is available for offline use, using the internal GPS of the user's phone. One of the best features of the app is the user submitted data. Users are able to leave comments to say if a certain water source is dry or running strong, or report on dangerous encounters they have had with animals, terrain, or humans. This allows thru-hikers to collect user submitted data on the trail ahead of them, allowing to be as prepared as possible for the hike ahead of them.
Most major thru-hikes are available for download as maps, with new ones being added each year.
