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.

So, what other good ones are around?