Hi there, Doug and thanks for getting in touch!
Great question. The PRO plugin does a lot of things, but booking appointments is not one of them at this time. We can create a calendar that allows registered users to create events (using our Community Events add on), but unfortunately those same members are unable to register attendees. That’s a great idea though!
I don’t have a specific recommendation in mind, but here is a search of plugins that might get you what you’re looking for: https://wordpress.org/plugins/search.php?q=appointment+calendar
Sorry I don’t have more to offer at the moment, but does this help answer your question? Please let me know.
Cheers!
Geoff