Magic Wormhole [1] also exists.

[1] https://magic-wormhole.readthedocs.io/en/latest/

And for a web native version, there's also WebWormhole: https://webwormhole.com/

Syncthing [1] also exists

[1] https://syncthing.net/

Syncthing is for syncing folders like Dropbox

It's not a good solution to send individual large files.

Syncing files is only one of its capabilities. It is best suited for use between two individuals/organizations that need to transfer files between themselves more than a few times. Its main advantage for me is that it doesn't require a central storage system, such as Dropbox, to hold the files. It's just you and me and a rendezvous server.

In a previous life, I used Syncthing to transfer terabytes of files from the company I worked for to a third-party printer. It was delightfully reliable, and easy to set up.

If it's a one-off, yeah, you're right that it's not wonderful. I've used Magic Wormhole successfully for that use case.

So it’s the GPG of file sharing?

Is there something like a Magic Wormhole server, so I can e.g host a file on my NAS (behind a NAT) for download long term?

also Keet: https://keet.io/

There's also LocalSend, which I've found works the best for me personally and is a bit more polished than browser clients

There's also croc: https://github.com/schollz/croc

croc has the advantage of being well-established by now. Most package systems have it.

I vibe coded this in one hour to send files to my work laptop. Static page + webRTC + short lived cloudflare durable object to make the handshake.

https://send.drexl.dev/

..also FilePizza as a web service: https://github.com/kern/filepizza

or tailscale's Taildrop as a native application: https://tailscale.com/kb/1106/taildrop