Syncthing is an amazing application which shares files between authorised machines securely. For me, I have all my files stored on my a dedicated server and all my other machines use syncthing to synchronise with the server and also the other machines.
To install syncthing easily on MacOS, the following commands needs to be run (making sure xCode is already installed):
$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
(entering your password when requested to do so)
$ brew install syncthing
$ brew services start syncthing
Syncthing will now be running and available at the url http://127.0.0.1:8384
For information on configuring syncthing I recommend you read the documentation found at https://docs.syncthing.net/intro/getting-started.html