Whoa, now that sounds like the use case I've been looking for since I jailbroke mine.

I have calibre set up to just email books to my Kindle, but that's an extra layer of indirection that I really don't need. I'll have to check that out.

I too have heard about syncthing for the first time today but from a different submission[0] you might care to be aware of.

Although, I realize Android != Kindle's OS, so I'm not sure how much concern there should be.

[0]: https://news.ycombinator.com/item?id=46184730 "Syncthing-Android have had a change of owner/maintainer"

If you have calibre, just turn on the wireless connection and have your Koreader connect to it.

https://github.com/koreader/koreader/wiki/calibre

Personally I'm most fond of Calibre + Calibre-Web, which masquerades as the Kobo Store and lets you use the built-in Kobo syncing mechanisms with your Calibre library instead of having to do it all within Koreader.

I've been experimenting with Syncthing on Kindle (https://github.com/Darthagnon/syncthing-kindle), but have had no luck seemingly because the Linux kernel included is too old and doesn't support network connections, or because the CPU is too weak.

Is there a project other than the one I forked?

I switched over to an Onyx Boox reader, so I don't have a Kindle anymore. But I definitely used the same project as you. I used a Kindle Paperwhite 11th gen. The linked project says it works with Kindle Touch, which is VERY old, so I don't think you're having network issues.

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!