Viewranger for finding myself on a map. I haven't used Buddy Beacon, yet, because I have other means of tracking myself and reporting my position back home, but I might use it someday. I'm not really into creating routes in advance, though, and still less likely to follow a route published by someone else (who, by so doing, has maybe made the route too popular). Expeditions require advance planning but for my day-walks I like to give myself the freedom to modify my route (usually just held vaguely in my head) as I go.
OS Locate for convenient one-off postion reports. It's also a handy way of recording spot positions for personal use; I can send them to myself and subsequently refer to them.
NOT OS Maps. I used to use this but it got more buggy with every so-called update until I gave up on it and uninstalled it. I won't reinstall it until I see some evidence that it has been rewritten by a professional.
Great Britain Topo Maps. A great range of maps is provided and I also downloaded OS maps at 1:25000 for the whole of Cornwall for a very reasonable price. They are shown with relief shading, which is a mixed blessing.
Locus Map. Installed out of interest, but haven't really made any practical use of it.
Earthmate. The companion app for my Inreach. More for tracking and messaging than for navigation; the built-in map isn't particularly exciting.
GPS Essentials. Essential for navigation geeks, like me. Lots of features to play with.
GPS Logger. A beautifully simple track logger, with all sorts of ways to report or publish the track as you go. Haven't done anything with it yet.
APRSdroid. A live-tracking app for radio amateurs only. Connecting it to my radio is still on my todo list but it will also work over the phone and I have used it often in this mode.
Map Tools. Converts position coordinates, e.g. Lat:Lon <-> OS grid. Will also calculate distances between given points in various coordinate systems.
ImrayNavigator. My sailing days are more or less over, I think, but I installed this because the built-in sample chart covers the whole of the UK south coast and it added interest to my day-trip to the Scilly Isles last year.
MC 50. A programmable calculator. I'm going to program it to calculate positions by resection, when I get round to it. Alternative to tryng to plot pencil lines on a map in the wind and rain! May come in handy for other things, too.