Favourite apps for iPhone that I might not have come across

[roselilylavender]

Following a conversation with a friend yesterday who was oblivious to reminders which led to me saying that I wished you could schedule sending WhatsApp messages and discovering that there is an app which does just that, I am wandering what else I might be missing out on,
Any suggestions?
As well as the standard ones for shops & entertainment, I love WhatThreeWords and the Merlin app.

You can turn your calculator into a currency converter. The rate won’t be exactly what you get as using banks and BDC the rates take commission and fees. I mostly use it to see if things are good value. ‘Hmm this is £25 no thanks’ or ‘£25 off a full steak dinner! Get in!’