I'm aware of at least two AFP client projects:
afpfs-ng and
afp-perl. Both support AFP over TCP, rather than over AppleTalk (i.e. the same as every macOS release has since Mac OS X Tiger.) Both are command-line tools that will run on macOS as well as BSD and Linux systems.
One question is whether your idea of an AFP client means full integration, where mounted server volumes appear in the Finder. That currently requires
FUSE support on macOS, which means installing a
3rd-party closed-source kernel extension. Apple has deprecated kernel extensions, but (unlike AFP) has not specified a cutoff release for them yet. MacFUSE would need to get rewritten as a userspace system extension at some point if support for kernel extensions is dropped. A project to do that was started a couple of years ago as
FUSE-T, but its development has been sporadic and it has some concerning open issues relating to data corruption and extended attribute support.
The AFP client in macOS Tahoe (26.0.1 as of today) still works fine, and given Apple's expected schedule, it will continue to work fine until the next major OS release in Fall 2026. But the clock is ticking.