Some months ago TOTD had the privilege to travel to the Isle of Wight on the bridge of the Fastcat ferry and was shown by my captain friend the Automatic Identification System. This listed the names, speed, destination etc. of all vessels above a certain tonnage in the vicinity. Well now you can view information based on AIS data for vessels throught the world. Zoom in on the world map, click on a vessel icon and you can view additional details such as ship photos, flag of ownership and estimated time of arrival at port.
[Thanks to AB for this suggestion]