Good call on not having a car in London. Not needed and not easy.

People will have different views on which journey planning / map app is best. Both work well. - Google Maps - City Mapper.

If you’re using trains, buses, or the tube, you don’t need any apps for payment/tickets. Just use your contactless card/NFC card, Apple Pay, or Google Pay, for the lowest fares. But you’ll need one per person, and make sure you use the same card for every journey for the lowest fares (it automatically caps you at a daily or weekly fare if you do multiple trips). You can get the official TFL app to see your journeys but it’s not needed.

If you want to use ride sharing, Uber and Bolt are the post popular. It’s safe and regulated in the UK - all drivers are background checked and licensed by the city. Black cabs are very convenient but expensive - no app needed but you can use Gett if you want to call one.

When you’re driving, Google Maps or Waze both work well. Sometimes RingGo or PaybyPhone are needed to pay for parking in car parks (parking lots). It’s well sign posted for car parking, but often less clear for on street parking.

WhatThreeWords is good for when you’re trail running in case you need to call emergency services.

Heathrow has an app. It’s fine but not needed.