I use the basics of Emacs Orgmode’s file format (without using Emacs itself) and then Orgzly on Android (https://f-droid.org/app/com.orgzly).

Thing is, I only really need reminders accessible from my phone, but do want my todo list synced to my desktop. I also want to take notes for my tasks, which is why todo.txt with its single-line restriction doesn’t cut it for me.

And then the nice thing about Orgmode’s file format is that it’s also really nice for writing larger documents, like you would do with MarkDown or AsciiDoc. So, that half-assed design document for my hobby project, I mostly wrote at the desktop, but also have it synced to my phone and viewable with Orgzly.

I use carnet on Android, available on Linux, for notes and to do list.

Useful list, thanks.