What does HackerNews think of maestral?
Open-source Dropbox client for macOS and Linux
(an unofficial Dropbox client)
Other commentators mentioned pihole/DNS, WireGuard, and music streaming, but you can also use them for a (slow) NFS server, persistent Syncthing node, Maestral host[1] (third-party Dropbox client written in Python (that can actually run on the Raspberry Pi, unlike the official Dropbox client)), or device that maintains a connection to a distributed network (e.g. Hyporborea/cjdns).
The client's UI is a bit odd, but at the end of the day it's really good at what it's supposed to do: Syncing files.
Performance is also great: I'm using multiple machines to write code on, and I keep my local git repo on Dropbox. I can literally save a change on my notebook and run it on some other machine 3 seconds later.
On Mac and Linux you might want to check out maestral (https://github.com/SamSchott/maestral), a third-party client that works really well.