What apps do you use for wildlife ID, walking in the countryside or for other outdoor or nature-based activities?
On my phone at the moment:
Merlin - bird ID by song or visually. I have never been much of a birder so rely on this quite a lot.
iNaturalist - general species ID from photos - astonishingly accurate overall.
iRecord - for submitting species records to the NBN.
Echo Meter Touch Bat Detector app - for use with Wildlife Acoustics plug-in bat detector, one of which I have access to sometimes, but most of the time I use my old stand alone Duet and ID the bats by ear.
Stellarium - astronomy app, great for stargazing.
AuroraWatch - for alerts to when the northern lights may be visible.
OS Maps - for walking using Ordnance Survey maps.
AlpineQuest - also for offline walking with OS maps, since I have a fairly extensive (if aging) collection of them in a format that works with this app.
Alltrails - which has a great library of walks.
What3Words - for sending locations to other people - including the emergency services. Speaking to a friend who runs the local county biological records office, he once told me that around a third of the records that he received had incorrect BNG grid references - so he was all in favour of what3words. OTOH I also know a boater with dyslexia - who far prefers lat/long or BNG: he find them a LOT easier.
iGeology & iGeology3D - for local geological mapping info.
I use Merlin as well. It's very accurate at identifying birds by sound but by pictures it's very hit and miss.
I use the BirdTrack app to record my bird sightings. The data is used by and helps the BTO (British Trust of Ornithology). As someone who used to play Pokemon GO it gives me a similar kind of enjoyment.
Merlin also allows you to record bird sightings but that data goes to the Cornell Lab of Ornithology in America instead. I tend to record my sightings in both, but only when I'm independently confident of my identification (i.e. not just plugging in what Merlin is telling me I'm hearing).
I think the RHS (Royal Horticultural Society) has some plant ID apps which I'm tempted to try out since I want to learn more about native plants/trees for my future gardening endeavours.