To use PIVKey on Mac OSX requires CCID support (for the USB tokens) and installation of PIV Middleware.
Mac OSX includes an (older) version of the PCSCLite CCID drivers. These drivers need to be configured to work with PIVKey. PIVKey has a utility to configure the CCID drivers. It can be downloaded here:
There is a wide variety of commercial middleware packages for PIV on Mac. In addition there is an open source package called OpenSC that supports PIV. OpenSC provides some tools, and most importantly a PKCS11 library, that allows PIV cards to be used by applications like Firefox and SSH.
There is an installer for OpenSC on Mac available here: