ACWW is a Nintendo DS game, like Animal Crossing, only you can use Nintendo WiFi to connect to other people. You can also use a local connect to do a "message in a bottle" deal, where messages you have in the ocean, will go to other people, and when they hook up to someone else, your message can pass to them (similar to a virus, but in a good way). More information about the game can be found:
Wiki ACWW entry
I will have something here... at some point...