I want to list briefly some of the applications while hiking. These are all android applications as I was carrying a Sony Xperia M4 Aqua phone.
So, I did carry maps and a compass most of the time as a backup but I really didn't need to reference them very often.
One of the most valuable on-trail resources besides the CDT Water Report were Jonathan Ley's Maps. These awesome maps contain his recommended route, a number of alternate routes, and most importantly a collection of notes from his own hike of the trail and update by hikers every year. This year, for the first time these maps were available as geo-references PDFs on the PDF Maps application. Meaning, that I could access the Ley maps, and notes from my phone instead of needing to pull out the hard copy to reference the notes. What I ended up doing was I would pack my hard copies of Ley's maps for a section in a couple ziplock bags and store them in a waterproof pocket of my pack and leave them there until there was some emergency that meant I couldn't use my phone. So, I had the maps but rarely needed to look at the hard copies, the phone was much more convenient.
This is a set of five paid applications, and mostly worth the cost (around $10 each). The biggest benefit of Guthook's over Ley's maps is the more detailed route information (but lacking alternates), and all the extra information included. Ley has some notes, but Guthook aims to be closer to a guide book, so it includes information (and pictures) about junctions and turns in the trail, water sources, campsites, elevation profiles, road junctions. You could hike the trail with just these apps and be fine. Though I wouldn't recommend doing so, there are a few major alternates included in the app but it doesn't contain some of the short daily alternates that Ley has, often these alternates give you more interesting terrain than the official route, or cut out annoying sections. I believe that Guthook + Ley maps is a perfect combination, Ley's notes are seriously useful to have and to review the trail immediately ahead, while Guthook makes navigation super easy.
This is another paid application that I found useful for navigation. Neither PDF Maps or Guthook let you load in your own trail information, Backcountry Navigator is a general purpose application so it does have this feature. As such I used it to load in the CDT's Water report, and Bear Creek Survey's Water information (Guthook is based on Bear Creek's information). Together these two sources gave me all the water information I needed. I also planned and took some alternates that were not mapped by any CDT resources: the Big Sky Alternate (aka. Super-butte Cutoff) and the Wind River High Route being the two main ones. Backcountry Navigator let me load those routes onto my phone also. One key feature of Backcountry Navigator was the ability to download and provide the base map imagery that it would use, so with this I was able to get satellite imagery of the trail ahead that I could look at to figure out future campsites and upcoming terrain in a way the topographical maps from Ley and Guthook didn't allow. I also took advantage of this to download statewide overviews so I could plan alternate routes in case of forest fires, or needing to bail from the trail. The final benefit was the ability to download town maps as I was often navigating towns on foot, this was nice to have to find my way around. Backcountry Navigator is a very much a do it yourself option so it isn't for everyone but if you are able to produce your own map files and trail information it was certainly an asset.
If I'm going to carry a phone I might as well use it to entertain myself a bit. Not related to the apps, but something I did, since my phone can take a MicroSD card is I had a 64gb card in my phone, and carried a 32gb card containing a bunch of media. Then if I wanted to watch or listen to something I'd transfer it onto the main card. This enabled me to carry a lot more videos (entire TV series) with me while keeping most of my device free for pictures and video I'd record.
I also tried VLC for Android but it crashed a lot (apparently this is better now but I have not tried), so BSPlayer Free met my needs pretty well. Its simply a media player that can play most types of videos, including many that the default players can not. One excellent feature is the ability to have pop-out videos, this is basically a little screen playing the video that shows up and that you can resize and drag around while using other applications. So I could multitask while watching a video, It also works with youtube videos, so I could load a long youtube video, like a debate into it, and browse the web while listening.
This is a paid application, but I think there is a free or trial version. While hiking, you can't really watch a video so I had to listen to something, I did carry some music, but I prefer more engaging content to pass the time on a boring road walk. Audiobooks worked well for this, but most audio players won't remember where in a long file you were, so using this player I could jump around different books or listen to something else and when I returned to the book it would remember where I was. That was the only feature I needed and this did it well.
For anyone wanting some content ideas, obviously there are plenty of books you can get in audio form, but another thing I did were lecture series, I used the following resources: MIT's Open CourseWare, OpenSecurityTraining (probably not interesting to most of you), The Modern Scholar and The Teaching Company. The lectures were great and give me a lot of good content to listen to, though I didn't find myself listening to anything but nature most of the time.
I like to read, I wasn't going to stop while hiking, so I had some PDF's of some books I wanted to get through. This worked just fine for reading, really not much to say.
Specifically, Spotify with a premium account. With a premium account, you can set playlists to be downloaded to your phone for offline listening. So, everytime I had good internet in town I could change my music library, and get the latest hits. I'm not much for listening to music but it was nice to have access to such a huge library of music, and not be locked into just music I downloaded before I left.
Free application, but requires a paid membership. I used Netflix a couple nights while hiking and amazingly had data, mostly this was my town entertainment. I choose a TV series that I would only watch while in town and was on Netflix. I never had to think about what I was going to watch, and I always had more episodes to go.
A catch-all section of random apps I found useful.
Amazon was a lifesaver, often there would be little sections up on a mountain where you could get service a couple days before getting into a town with service. So with Amazon Prime, I could order something (like new hiking shoes) and have it at my hotel when I arrive. Using the app was much better than using the website when the data connection was slow. Also, if you, like me are not from the US and find the cost of Prime to not be worth it, there is now a monthly instead of yearly prime membership which is much more reasonable for a hiker only in the US for a handful of months.
Last year, I had a lot of issues trying to upload photos as my phone would crash when using websites to upload my weekly photo dump. I eventually started using Google Drive to upload but it would randomly stop uploading, and getting links for the blog posts was rather difficult. So, I took to hosting the images myself to do this I used FSync with a Sync job that would sync the Camera folder on my phone to this website. I never had any issues uploading with this.
Simple application that would use my GPS information and let me know the various sunrise and sunset times. Simple UI and does what I needed. It was great to have some idea when it would start getting dark and how fast the sun would be setting. Knowing sunrise also helped plan some of the longer days.
Sometimes I would download some large files while on a not-so-great internet, a download manager was useful to handle to frequent disconnects.