The two players, blue and red, take it in turns to place
pieces on the board. You can place a piece either on a blank
square, or on a square already occupied by some of your own
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
That player's the winner!
To help you, squares that only need one more piece to
explode are colored slightly lighter.
And a challenge
When set to "not so thick" mode, the computer player is pretty
good. If you can beat it regularly (or indeed at all) then you're