Registered to Now Software's Now Up-to-Date calendar server; a dead classic-Mac product.
IANA registers 3168 as poweronnud, "Now Up-to-Date Public Server", from Power On Software's Now Up-to-Date & Contact — a shared calendar and contacts product for classic Mac OS and early Mac OS X. The product and its vendor are long gone and there is no protocol specification in the public record, so the registration is essentially the whole story. Nothing you are likely to run listens here today. If 3168 is open, treat the scanner's poweronnud label as noise and fingerprint the service.
Expose with care
An open 3168 is an unidentified listener; find out what it actually is before deciding whether it should be reachable.
$ nc -vz TARGET 3168Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.