Unassigned at IANA, at the start of the 6779-6783 free block.
IANA lists 6779-6783 as Unassigned, and nmap's service database gives 6779 no name. No standard protocol, no vendor default, nothing documented squatting here. A listener on 6779 is an application that took a free high port, and the port number carries no information about it.
Expose with care
Treat as unidentified software until you match it to a process on the host.
$ sudo lsof -nP -iTCP:6779 -sTCP:LISTENSeen 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.