Let me tell you something as a person who is constantly looking for a better solution for note taking.

The holy grail is a wiki.

I've tried Evernote, Google keep, simple notes, Google docs, one note, even a series of word documents.

I have never been more satisfied when I set up a personal wiki at home and forwarded it online. Wiki of choice is dokuwiki. It's very well documented, and simple to set up since it does not rely on a database for storage.

Let's go through the features: * Universal access? Check. Just type in my IP (or host it for cheap at a place like feral hosting) I have access. Could be a complete stranger's computer. * Security? Yep. No public access, got two accounts, one is read only for an untrusted computer. All the data is in your personal control. * Mobile accessories? Yep! Dokuwiki automatically formats itself for mobile browsing * Cost? Free! If you host it yourself. Hosting sites generally start around $10 a month, but dokuwiki uses very little bandwidth, so private hosting is fine * Syncing features: since all edits are done to the server, it all instantly syncs.