The Etherwave AUI device shown (the skate/triangular one) is what I'd classify as "maybe uncommon, but not particularly rare" - there's plenty of them hanging out in the Re•PC in Seattle, as an example. I've got a few, some are plastic and some are metal, sizes varied a little bit. They are convenient for the reason that you can string a few systems together without a hub or switch, or hang a few off a single hub/switch port.
The Mac/PB is interesting. I would initially have said it looks like a local talk to ethertalk bridge which, again, are "maybe uncommon, but not particularly rare" but it actually does look like it's more straightforwardly a serial-connected network interface. That could be really handy in a different way from a normal ET/LT adapter. It's definitely a neat find.