I have been building an iOS net worth tracker app as a side project for more than 5 years now:

https://www.percento.app

I was an accountant for 3 years before I switched my career to be a programmer, then I kept coding for 10+ years in big tech companies and had always wanted to build a product on my own. Eventually, I found the niche to combine my finance knowledge and my iOS skills into this App and happily building for a few years.