Payback keeps track of money between people, across currencies and part payments, so you never have to reconstruct it from memory or a notes app.
Free on the App Store

Every balance owed to you on one screen, converted into a single running total.

What it was for, what has been paid, and what is left, per person.

A record of every repayment, so the same debt never comes up twice.

Note how something was settled, not just that it was.

A nudge when something has been outstanding too long, without you chasing it.