Each team consists of two players. One is the "recommender" and the other is the "chooser".
Before B's move, B team's recommender nominates one move, and the recommender of W also nominates a move. Both choices are presented to B, and he chooses one of them. Then, for W's turn, the two recommenders choose moves and W chooses, and so on. So at any point the chooser chooses between just 2 moves - one of which is good for his team, and another which may be a cunning trick. While the recommenders are thinking, both of their team clocks are running. Once both potential moves have arrived, the chooser's team clock runs.
Play as normal, but after every move, you can nominate one move as "forbidden" for your opponent's turn and they cannot play it.
As choices above, but with only 2 players - one player nominates two moves, and the other team chooses the least bad one. Then they switch roles. This game would not be fun.
As your move you can either play a move as normal, or slide one of your opponent's stones one space
This is a really interesting four-person game. The board is divided into quadrants which overlap on the K line and the 10 line. Each person is assigned one corner. They are allowed to play anywhere on the board, except the opposite quadrant. Play proceeds in a circle within the 4 players.
It's interesting because within your own quadrant, you are really strong - on the two edge quadrants, you are not quite as strong, because you can't run towards the one forbidden area.
There are also scary team-ups the other 3 players can do against you - your groups need to be really safe if you are leading.
It was invented by Jon at a meeting of the Beijing Go Club.
Another variant might be to assign one half of the board to each player - so you would have less total area to play in, and would only interact with the two neighbors, not with the person who sits opposite you (except on the dividing line, which would be shared)
As normal go, but scoring is 1 point for each independent living group at the end of the game. There will be lots of cases where you won't want to connect.