It's on my todo list (in trello :) ... but haven't got to it yet.
I use a combination of Unison(-gtk) and Foldersync (android) to replicate some quite large data sets between desktop, server, a couple of laptops, and tablet & phone. Keybase and Synthing are definitely on the list of potential replacements for the manual, periodic sync.
How does Syncthing go insofar as replacing a note-taking system (tagging, collaboration, etc)?
There isn’t any explicit notion of collaboration, and tagging can be accomplished by way of a folder structure. I haven’t tried symlinks, which is how you’d make multiple tags work on a regular file system.
Syncthing’s purpose is to ensure that a specific directory remain synchronized across multiple computers and/or mobile devices. It accomplishes this goal with the minimum of fuss, and (in my experience) works better than Dropbox in that it burns fewer CPU cycles and doesn’t crash/hang/nag me to upgrade.
I think when I looked at it a while back my concern was how it would cope with one or more of my devices being off-network for days at a time (a regular occurrence).
The other devices wouldn't be, and changes would only be done wherever I happened to be, but the cost of evaluating this solution was unfortunately higher than not making any changes. As I say, it's on my list. The suite seems to be quite robust - but given Evernote's primary stated purpose was to ensure none of your data was ever lost (and yet many people have sad stories of data loss) I'm extra-cautious about changing my workflow.
Actually much more pedestrian than that, as I'm confident it works on cases more complex than me. It's simply that I've got a series of mechanisms that work acceptably, and it takes time and effort to run up a VM, set up an archive process, test a new suite & workflow over several weeks.