This is just AIS Live. AIS (Automtic Identification System), or UAIS (Universal AIS) is now required by law on all vessels over 5000 tonnes. The original idea was to help prevent collision at sea under the SOLAS (Safety of Life at Sea) convention. It uses self-organised time-domain multiplexing to broadcast GPS Lat/Long (usually WGS84) and current SOG (Speed over Ground) and COG (Course over Ground), augmented by heading, cargo, port of departure, next port of call, and waypoint information.

It also broadcasts the ship name, registration number, physical size, tonnage, loading and other information.

Interestingly, although it's required by law that it be carried, it is not required by law that it be turned on.

Note, the above is all from memory, and some may be a little out-of-date or inaccurate. It's close enough to give you the idea, and if you want more accuracy it's easy to look up.