A long time ago my friend Mark (who, regrettably, I have long since lost touch with) showed me a game he had written on his Amiga (the original rules available in the Criticality options are pretty much the same game).
Over the years I've written a few variants on the game whilst learning different languages and frameworks, but this version introduces some significant differences.
Critical - a square with as many pebbles as neighbours has reached critical mass and will explode sending a pebble flying out to each of the neighbours.
Super-Critical - a square with more pebbles than neighbours is super-critical, after exploding and sending a pebble to each neighbouring square the remaining pebbles implode and destroy the square removing it from the game.
Hyper-Critical - a square with significantly more pebbles than neighbours is hyper-critical. The mass of pebbles is so great that an explosion does not occur, instead the pebbles implode, destroying the square and removing it from the game.
The following game types are provided:
Original - Criticality enabled, no super-criticality or hyper-criticality. Games often end with the explosions stuck in a repeating loop. Pebbles can be placed on any square not occupied by an opponent. Last "man" standing wins.
Standard - Criticality and super-criticality enabled, but no hyper-criticality. Games often end with the destruction of the entire board. On the first turn pebbles can be placed on any square not occupied by an opponent; on following turns pebbles can only be placed on squares occupied by the current player. Last "man" standing wins.
Scored - Same as standard game, but scores, both positive and negative, are assigned to different effects. Highest score wins.
Custom - rules can be tweaked to suit