Netatalk is a Free and Open Source file server that implements the
Apple Filing Protocol (AFP) 3.4 over TCP/IP and AppleTalk ddp.

AFP is the primary file sharing protocol used on Apple II, Traditional
Mac OS, and Mac OS X, as well as one of several supported protocols on
macOS.

If you have a local network of macOS, Mac OS X, Traditional Mac OS, or
even Apple II computers, running a Netatalk AppleShare server allows
you to share, collaborate on, and back up files comfortably.

The latest macOS at the time of writing ships with an AFP client, so
Netatalk can act as a seamless bridge between new and old Macs. With
dnsd support, the Netatalk AFP server will be auto-discoverable via
Bonjour. It supports Time Machine backups.

Compared to cross-platform file sharing protocols like nfs and sftp,
Netatalk delivers a Mac-like user experience,

Compared to a Samba setup with macOS support, Netatalk comes with a
lot less complexity.