The once-dead Expansion Slot utility application has appeared in the latest beta of macOS Catalina, currently available to registered developers.
It is used for configuring, adding and managing PCI-cards, meaning that Apple will release it for the unreleased Mac Pro, that will be configurable. It has eight PCI slots in total.
Expansion Slot Utility for macOS, still has the same name as the pre-2008 version. It was discontinued with the old Mac Pro in 2008, and Apple has relaunched it as ‘version 2’, over ten years on.
The application also has new iconography of the Mac Pro, and 2019 copyright information.