I want my notes as plain text files (or Markdown files to be specific), and I'd like to sync them with my phone. I'd also like to use the text editor of my choice to edit said text files. Cool, I just install Dropbox on my desktop, sync the files, and edit the files with Sublime Text. Oh but huh -- I can only edit the files on my phone using the Dropbox app, which doesn't work when I'm offline or have spotty reception.
I install Syncthing on my Windows PC (it runs the syncthing.exe on startup), install Syncthing and Editor[1] on my phone, and bam, now all my notes are synced directly to the filesystem of my Android phone and editable by any text editor I choose. As an added benefit, I still have a cloud sync on my PC, so the files are still backed up to a cloud service!
[1] https://f-droid.org/en/packages/org.billthefarmer.editor/