What do you wish you had an app for? Is such an app possible?

I wish there was an app you can schedule every appointment though. I know certain businesses use apps to schedule appointments. But I want a singular app where you can schedule everything though. That way you do not have to make a bunch of phone calls or write the appointment time on a piece of paper. A piece of paper you are going to eventually lose before the date of the appointment. I think that would be really cool and help organize a lot of people’s lives. Sadly I do not think it would be possible. I do not think every business would do it unless somehow Apple or Google did it. Even then there would be some outlying businesses.
Another idea is an app that tracks exactly how and where you spend your money. I am not sure if this app already exists. Even if it did not you could easily make an excel spreadsheet. It would just be very tedious and time-consuming.