This is crazy and genius at the same time. TwitchPlaysPokemon started 4 days ago and has now become a viral game with over 35,000 players all playing at the same time.
The way it works is that the character is being controlled by the people who post comments. Users have to post corresponding buttons such as up, down, left, right, A and B to make the character carry out actions. The channels creator then worked out a way to turn those comments into actions that happen in the game.
The game being played is Pokemon Red/Blue. It started off small with a few players playing together and they amazingly have beaten half of the eight gyms leaders in the game. But now there's thousands of people commenting all at the same time it has become basically impossible to do anything - it's pretty hilarious.
The developer said he's going to let the game run 24/7 until it's basically complete but he has little faith in that happening.