Station wagon full of tapes.

Exposing it over HTTP ensures all can access, but that's my best solution. I don't know what your intentions are, or what your pain-points are, or what you're willing to deal with, or what your data is and if it poses a risk to you personally to have it exposed.

SFTP or WebDAV would work.

Surprised no one just said Samba or NFS over a tunnel (Tailscale, WireGuard, etc).

Or by “sharing” do you mean keeping files synced between the two for replication?

Flash drive in person.

They take what they want, you do the same. Boom both are better off.

Rsync

We use Tailscale to share between accounts.

But for large transfers I use an encrypted HDD.

For large volumes of data, nothing beats shipping a large external drive (with a fast interface) from location to location.

SFTP has been mentioned and is a good choice but this could also be done over torrents too. It’s the other most common legal use besides Linux distros.

If you want to run a mirror, rsync over ssh is one of the simplest ways.

You could also set up a jellyfin (for media) or gameyfin (for games) container, expose that to the internet and give them credentials.

You could set up a tunnel between the two.. a job that rsyncs a folder to the other server automatically when something is added.

Just a thought.

If you're wanting to share all files, many of the methods already mentioned work well. If you're wanting to share specific files, CopyParty is a good way to go.

LAN party!! You have the optimal excuse to make one happen ;)

You can't beat the bandwidth and reliabilty of mailed ssd's

Get 'em in the same room together, put on some Barry White, and let the magic happen.