It sounds like the events they have in Guild Wars 2 from what yoshi said. There is an announcement that an event is nearby you go there, text appears on the side of your screen giving you an objective and sometimes there are who will run up to players or you will just hear them as you pass, screaming about whats happening (bandits are attacking the farm! escort out supplies from point a to b. So and so's apple farm is overrun by spiders, exterminate the spiders and deliver so and so fresh apples -all from GW2 btw).

You go to the appointed spot, after a minute the event starts and is scaled to the amount of participants, everyone fights the same mobs, heals each other, raises each other, etc etc you complete the objective, pass or fail, and you are rewarded based on your level of participation. Its a fairly good system as long as the event doesnt remain exactly the same and on a loop which is a flaw to the gw2 timed events. I mean how many times can a farm be attacked by bandits in a day.

Even though I havent really been able to get into gw2 this still makes the world feel more alive and makes you feel your more of an active participant in that world.