What sort of data? I’m also building a service to do this for database backends. This was the side project to move files around whilst I was working on the other one!

It's a rather fancy contact database, meant to handle sensitive/confidential data safely.

Codeberg.org

Greet-and-Grow

A powerful, offline personal CRM app built with Flutter, with custom features for fundraising, ministry, sales, and personal use.

I had originally pictured letting users choose a cloud storage folder they're comfortable with, and storing the app data there so multiple devices could use the same data. But that's frowned upon because of all kinds of sync issues. I'm curious to see what you come up with! For now I'm aiming for Android, but the code is written for any platform, so hopefully it will end up on iOS, etc. too.