The elegant simplicity of Tetris may be impossible to improve upon, but that hasn't stopped the developers of Sandtrix from trying. The game starts off like Tetris, but the familiar blocks are subject to sand physics and crumble upon landing. With no need to get the pieces to fit, the challenge then becomes to form a contiguous stretch of color from one side of the screen to the other, in order to remove material:

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At press time the game was playable online here, but it likely won't be long before The Tetris Company, Inc. intervenes and has it taken down. And I'm not writing Sandtrix up as an endorsement of unauthorized variants, but rather as an example of a creative way to re-think established mechanics.