Copyright (c) 1997 Peter Hartley

This game is played on an the following board (in fact, you can play it herein!):

TURN - On each turn, each player places a stone on an empty cell, or over a friendly stack.
When the number of pieces on a square reaches the critical mass for that square (two for corners, three for edges, four elsewhere), that square explodes, and scatters the pieces on it in all four directions. If any of these scattering pieces lands on your opponent's pieces, they are captured and become yours.
If this scattering causes other squares to exceed their critical mass, then they explode too, and so on, until either the explosions stop or there are only one player's pieces still on the board.
GOAL - The player that removes all enemy stones off the board, wins.

In the applet, to help players, stacks that only need one more stone to explode are colored slightly lighter. This game is not adequate to play on a real board, because the chain reactions can be very long.

An example

Red's turn. If he plays at the marked cell, the cell (already with 3 atoms) will reach a critical mass of 4 and will explode!

The explosion will create 98 (!) chain reactions and will evaporate all blue atoms from the board. So, Red wins!

There is also a ZRF to play Automaton, also known as Atomic with Zillions.