Registered as Trusted Web, one of a pair with 3012 (Trusted Web Client), and rarely seen.
IANA registers 3011 as trusted-web and 3012 as twsdss, "Trusted Web Client" — a server/client pair from a 1990s commercial product of that name. No public specification survives and there is no maintained implementation, so the names outlive the software. A listener on 3011 today is almost certainly an unrelated application that grabbed a free port.
Expose with care
"Trusted" is a product name, not a property of the port — find out what is actually listening before treating it as safe.
$ sudo lsof -nP -iTCP:3011 -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.