Copyright (c) 1996 David Boll

The game starts at a NxN square board, (let's say 8x8) with the following setup:

NEUTRALS - There is a 3rd piece, a neutral stone, that can be moved by either player.
MOVE - Each stone moves on a straight orthogonal line any number of empty cells.
FLIP - If a move results in exactly two types of pieces being orthogonally adjacent, they are all flipped to the third type.
KO - A board position cannot be repeated.
GOAL - If, at any moment, a player has no stones of his color or cannot move, he looses.
An example

Black's turn. He slides f3 to cell [a], turning itself and the red soldier into neutral pieces. 

Now, Red does not have any neutral moves that creates new red stones. But his remaining stones at b1 and e1 are under attack.

There is a ZRF to play Boll's game with Zillions.

David Boll's rules leave some open ground about the Flip mechanism. There are a lot of other cases that the rules does not say anything (and so, nothing happen on those cases). The other cases are:

  1. The stone is adjacent from two or three stones of the same type;

  2. The stone is adjacent from two stones (3 cases) or three stones (6 cases) of different types.

A possible variant is to see each pair of stones has a specific case of the original flip rule, but just changing the other stone, while the moved stone would remain unaltered. Of course, other variants are possible. The point is to make the game more dynamic, avoiding lots of non-flip situations.