UDXF is the Utility DXers Forum. The forum is centered around the exchange of news and information relating to "utility" radio stations and signals, below 30 MHz.
What kind of stations are covered? Actually everything in the range of 0-30 MHz with the exception of Broacasting Stations, Pirate Stations, and Amateur Radio (with the exception of utility related activities).
If you are listening to the stations mentioned below, then UDXF is the place to be.
Maritime stations, both coastal stations and ships
Aeronautical stations, both ground stations and aircraft (voice, HFDL, Selcalls, Volmet, etc.)
Beacons (NDB, Driftnet beacons, Propagation beacons, Pirate beacons, Hi Frequency beacons, etc.)