Setup is the same as normal - two players. To start, both players decide where they want to play. When they have decided,
they place their stone on the table (but not on the board). When both are ready, they say "go" and put the stone on the board.
If they collide, they both take the stone back and that place is now "forbidden" until another area has been played in.
If there is no collision, then life/ death is evaluated. black / white stones can die simultaneously.
The game works pretty well, except sometimes there are big clusters of forbidden areas. I'm not sure if the endgame would be as fun as the normal game.
5-in-a-row also works this way, and works somewhat better. There's some fun guessing & interesting strategic thought.