An Apple registration from the AppleShare IP era; you will almost never see it live.
IANA lists 687 as "asipregistry", registered by Erik Sea of Apple during the AppleShare IP period. It was a registry/lookup companion to AppleShare services, not the file protocol itself — AFP has always run on 548. No public protocol specification was ever published and modern macOS does not open it. On a scan it is effectively noise: either a very old Mac server or an unrelated service squatting on the number.
Expose with care
Undocumented and unauthenticated by any published spec; if something is listening here, identify what it actually is before leaving it reachable.
$ nc -vz TARGET 687Seen 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.