So I've made an app, specifically ReminDiary. It's pretty basic, but it fills a niche.
The premise is simple, write a daily diary entry, and once you've done that for a while it starts reminding you of previous days. I know people that have been doing this for years and years and once they've imported their data they get a nice view after each day's entry about what was happening on this day 1, 2, 3 ... x years ago- it's quite fascinating really.
Some things I aimed for on this: There is no cloud- it's all just kept on your local device, but if you backup your device (most androids have this built in to some extent) then backups are taken care of. If you don't like that though you can easily export the data in CSV. On the flip side, you can import a CSV of any data you have. Point being- I don't want to lock you in or out- it's your data, you take care of it. Next- it doesn't phone home, in fact, fdroid doesn't even tell me how many people have installed it. I added an optional anonymous telemetry option which is off by default, but you are free to turn on if you so choose, but otherwise I have no idea how many (if any) people are using it. This goes both ways though- if you'd like changes or like it- please tell me.
Finally, it's on fdroid, not google or apple: There are a couple of reasons for this, mainly privacy and not giving in to big tech. If I get great feedback I might have to consider putting it on the play store, but for now fdroid works and makes me happy, so there it is.
Anyway, I hope you enjoy it and find it handy if it's your cup of tea.
Be ReminDiary-ing (sorry)