This app keeps track of what you eat and your workouts. Take a photo of your food and it estimates the calories, or look the food up, or type the numbers in.
There's no account. Everything is saved on this phone only.
This works out how much to eat each day. It's a starting estimate, and you can redo it anytime.
You can change these anytime: tap the gear at the top right, then Work out your targets.