Copyright (c) 2002 Chris (original idea)
Chris and Joćo Neto (actual rules)

In Crowd is played on an empty NxN (say 9x9) square board:

PHASE 1 - On each turn, each player drops a stone on an empty cell not adjacent to any stone.
When a drop in this conditions is not possible, phase 2 starts.
PHASE 2 - One each turn, each player passes or drops a stone on an empty cell.
After the drop, any (orthogonal and diagonal) adjacent enemy stone changes color if a majority of its neighbors (including itself) are of the opposite color.
This can result in a chain reaction that can flip the neighbors of the neighbor if the majority of their neighbors are now of the opposite color, and so on...
If a stone is placed and does not produce any color changes and a majority of its neighbors are of the opposite color, then the just-dropped stone changes color.
Note: If the number of friends are equal to the number of enemies, the dropped stone does not change color.

GOAL - When both players pass, wins the player with more territory (use Chinese Go count rules).


An example

On this position, all cells are adjacent to a stone, so the game goes to phase 2.  


After the threat a4, White replies b3,  then a2, c2. Then Black's b4 flips a3 which flips b3.

Some words from the author: [...] The capture by majority idea came to mind because I was trying to think of a novel way of playing Othello--the parallel between Soucie's Lines of Action and Sackson's Fields of Action is obvious. The isolationist move constraint was merely an idea to prevent the pieces from crowding at the beginning, and seems like a happy accident. If nothing else, it results in interesting, novel (and aesthetically appealing) starting positions. As opposed to, say, Go, it seems that in the above rules, opening moves are critical--they may determine the entire game--and moves become less and less important, until at the end, you are just "filling in holes". For this reason, I'd like to play on a larger board.[...] The overall game itself isn't terribly interesting (unless I am not appreciating it fully yet)--it may actually be trivial, with the only necessary strategy being to make the maximum number of flips, though this still leaves the opening to be fought over--but it is novel and worth thinking about, maybe improving, and definitely trying on a larger board, which may give rise to some interesting middle-board battles. 

Also check Pleiadis, a related game.

Invincible positions

Like in Go, the tactics depends if the action is on the corner, on the edge or on the middle. These structures cannot be captured.

A strong middle structure

Based in the previous middle structure, these stones are very powerful, since White cannot attack them from the inside.

I wish to thank Jorge Nuno Silva for game playing and some good suggestions.