[anoncake]

I use Org. It's part of Emacs, which you may consider either a dealbreaker or a feature.

While Emacs itself does not really work on mobile (unless you run it in a terminal), there is a companion app for Android called Orgzly. Unfortunately it is quite limited. For example, it does not support tables. (Since Org files are plain text, you can view and technically edit them, but the latter is a pain.) It's good enough for taking quick notes so you don't forget them and to look at existing ones.

For syncing, I use Syncthing, which works flawlessly. Conflicts have to be resolved manually though. Orgzly also has built-in support for syncing via Dropbox. I've never used it as it involves manually pulling and pushing to the server as in a VCS rather than working in the background.