Radarr's web UI — the movie half of a home media automation stack.
Radarr, the movie collection manager for Usenet and BitTorrent, defaults its web server to port 7878 (its configuration provider falls back to 7878 when no port is set), which places it beside its siblings Sonarr on 8989 and Prowlarr on 9696. IANA's registration for 7878 is owms, Stonebranch's Opswise Message Service, but on a home server or NAS the overwhelmingly likely occupant is Radarr. The UI is plain HTTP unless the operator configures TLS, and the same port serves the REST API used by the rest of the stack.
Do not expose
The web UI is a full admin plane — it drives downloaders and writes to the filesystem — guarded by a single API key over cleartext HTTP by default. Reach it through a VPN or an authenticating reverse proxy, never directly from the internet.
$ curl -sI http://127.0.0.1:7878/Seen 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.