The game itself is a pirate adventure, in which players move from island to island to buy, sell and fight for goods. Depending on where you are in the physical world, you'll find different islands, different market prices and different ships to fight.

http://areacodeinc.com/work/plundr/
http://www.joystiq.com/2007/06/04/plundr-first-location-based-ds-game-debuts-at-where-2-0/
Another application is advertising, in this case, for the Discovery channel. The online/mobile/oceangoing game allows users to create their own vessels, choose an affiliation with one of three marine-research organizations, and track flesh-and-cartilage sharks off the West Coast. That's right, real sharks swimming around with GPS devices on their fins -- telemetry data provide the sharks' real-world locations on the game-play map.

http://dsc.discovery.com/convergence/sharkweek/shark-runners/shark-runners.html

Ah, the mastermind of the above games, and many others, is this cool company http://www.areacodeinc.com/

These applications work because the virtual and real worlds crossover, and because users can participate in either world and see the results of their actions in the other. In Plundr, if the machine tells me that only if i walk to the end of my corner, ill find an island where i can buy, sell and fight for goods. I then need to actually physically move somewhere else before advancing in the game...so the game is a combination of virtual and real world messages, actions and outcomes.
These kinds of games - often coupled with other networking or "viral"
components where users interact with each other - are becoming extremely popular for use not only in pure entertainment but also in advertising because they engage users