Unassigned at IANA, with no widely used default service.
IANA has no registration for 8290 on either transport. Nothing common defaults to it, and a listener here is a local choice. It is worth not confusing with 8291 one number away, which MikroTik RouterOS uses for WinBox management — also unregistered, but genuinely common on network gear.
Expose with care
Identify the process behind it; if you are scanning network equipment, check whether 8291 is open alongside it.
$ sudo lsof -nP -iTCP:8290 -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.