For example, your use case sounds like the ideal scenario for Settle Up. Me and my 2 closest friends have a running group where we annotate expenses and there's always a clear picture of who owes what amount and for what reasons.
Of course, tiny customizations like a dog's picture per month, are not possible to do with a 3rd party app :-)
So, yeah - but micro tools are a thing.
That’s till some product manager decides they want metrics to go up, and the app starts spamming you notifications multiple times a day, or tries to shove in your face unnecessary financial products, and starts selling your transaction data with the hope of increasing monetization to keep their overstaffed teams…
A home-cooked app from someone you know/trust seems much nicer than that.
My GF and her Sister kept a running tab (Beans) between them - and always were having issues reconciling who owes what for when etc...
These are smart and capable women, but for some reason their personal tab between eachother was a headache - so an "app" I made was just a smarter spreadsheet in google docs they share and they enter their info each month and it tallies who owes what.
I forgot about it for over a year or so - and so I asked my GF is they were still using it
"We use it all the time - its been such a lifesaver."
Its literally just how one would use any spreadsheet... these are high-paid, highly successful people, and were struggling to just get a 'tab' thing going.
One of the things I did, was have it load pics of their shared dog on each new tab (a tab per month) and they loved that.
Silly, stupid, took me 15 minutes and they have been using it for the last couple of years and love it.
But yeah - build little tools for a small circle.