I'm thinking of logging on, concealing my computer, and trying to get a sense of all the devices available to me. I'd love to do it from OS X...but I would be willing to use a NAT-enabled Kali Linux if I have to. I'm not a pen-tester, but I feel like a pen-testing tool would accomplish the diagnostic I'd like.
Have you looked at nmap? It quickly identifies all devices, ports and IP addresses on a network. But you should use it only on your private IP address range.