You can also run Syncthing on a jailbroken Kindle. That opens up a world of possibilities!
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Is there a project other than the one I forked?
It's been a while, but I think I enabled SSH on my Kindle and set it up that way. I started Syncthing via KUAL, then used an SSH reverse proxy to configure Syncthing on my laptop.
It -was- kind of a pain, but once it was good, it was good!