This has hit the internet by storm! There is a fighting game called MUGEN which hosts about 3000+ characters and the AI fight it out in random battles.
A clever guy took said game and streams it on his website saltybet.com and made a casino out of it with a leaderboard.
Players bet to see who will win each fight and based on the odds the fighters get, determines the payout. Players cant see who bet what until after the timer runs out. Chatting is used to "juke" players into betting on the wrong fighter.
It's probably the most addicting idea/game I have ever played. I highly suggest checking it out, this will be viral eventually when the word gets out. There is already 5000-6000 players 24 hours a day 7 days a week.
Uh........................................Salty Bet isn't an mmo, it's not even a Browser mmo or anything of that sort. It's just like an internet game at best.