Tetris
by Sergey Smolyachenko
With an executable size of only 844B (the archive is actually a bit larger than the file it contains), this is probably not only the smallest Tetris clone (less than half the size of either Small Tetris or TinyTris), but the smallest game in general I've ever come across.
The price for the small size is the lack of any eye candy like color, but that in turn makes it, along with Diamaze, one of the very few games that can be played on any PC ever built with equal enjoyment. It uses 40 column color text mode, if you are playing it under Windows in a window, set it to an 8×8 font, which will give you square albeit tiny blocks.
