There is self-hosted PHP app named Firefly III [1] that supports double-entry bookkeeping system. If by "sharing" you mean "logging on your account at different computer/phone" then it should work. There are user accounts, but only to use same installation without sharing data.

[1] https://firefly-iii.org/

Disclaimer: I'm just a happy user, who reported some issues and pull-requests.

This deserves more attention. Thanks for Firefly.

I keep my GnuCash file in an encfs-encrypted Dropbox Folder. As long as you don't try to edit it from two devices simultaneously, this works quite well.

I'll second the opinion for Dropbox. GnuCash has lock files, so you can open read-only if it is being edited by another person to avoid conflict.

How do you deal with multiple currencies and expenses?

I find duplicating expenses accounts (national currency + USD for international shops) very tedious.