PMOG is short for "Passively Multiplayer Online Game". Like most MMORPGs, you play at the same time as a tremendous other individuals and collect STUFF and gain points to LEVEL. Unlike most other MMORPGs, however, you only play PMOG passively. This basically means that you play while doing something else.
PMOG is played by running an addon for Mozilla FireFox. While you surf, you can interact with pages in ways defined by the PMOG game. Every unique site you visit gets you points (datapoints). You can run into mines laid by other players, which takes away those datapoints. Of course, armor will shield from those mines and St. Nicks will attach to a player and destroy one mine that he tries to lay. Then there are portals, which allow you to set up a hyperlink on a site that will take a person to another site of your choosing. Finally, there are lightposts, which you use to make a "mission", a path between several related websites with a bit of text to explain the connectsions between them.
The artwork and the text are in the "steampunk" style, the interaction with your regular browser is very subtle. All in all, it looks to be an interesting way to sort of semi-play a game, while mostly just wasting time on the web in all the ways that you may have already been doing. (though, truthfully, there were a few websites that I now have in my regular bookmarks that I have discovered from the missions. Do I really need more websites to check out?)
More information is available at their website of http://pmog.com