P.M.O.G stands for passively Multiplayer Online Game, as you can see.
It comes in the form of a Firefox addon. You gain experience by visiting different websites. And you can create and participate in different missions in which you visit groups of related websites, or find them. Malicious players can lay mines on websites to hurt those who visit it, or white-hat players can lay "St. Nick" items on the websites to latch on to visitors and protect them from mines.
There are, of course, many different kinds of items, weapons, and armors... along with many other features.
Not much else has been released about the game, but you can get more information here:
http://www.gamelayers.com/pmog/
It's currently in closed beta but you can get an invite from inviteshare.com or you can leave your email on their site at:
http://www.pmog.com/
