Copyright (c) 2006 Nick Bentley
rules adaptation by Joćo Neto & Bill Taylor
Product is played on an empty 5x5 hexagonal board:
- GROUP - A connected chain of friendly stones.
- TURN - Initially, Black drops one stone of either color, then for the remaining turns players drop two stones of either color.
- GOAL - After the board is full, wins the player with the higher product between its two largest groups.
- If both products are equal, wins the player with less stones on board (note: draws are impossible).
Black's turn. Right now he has 21 points (7 stones for his largest group, and 3 stones for the 2nd largest. He decided to connect the largest group with the isolated stone (moves ). With this move he gets 30 points.
However that was a bad move. Now White simply plays two black stones at  connecting all black stones into a single group. So, the actual score for Black is not zero (his 2nd largest group does not exist, ie, is made of zero stones).
It will be impossible for Black to create another isolated group without White's help.
Check the author's blog: http://nickbentleygames.wordpress.com/2013/01/11/produto-game-published/