Nyet

Nyet was probably the first Tetris clone (for the PC; there were several for 8-bit Atari) in the sense that it did not intend to change anything from the original Tetris, though it was willing to improve it:

Tetris

I claim no credit for inventing this game; that was apparently done by A. Pajitnov and V. Gerasimov in the Soviet Union. They called the game TETRIS. My version of the game was originally also called TETRIS, but has now been renamed NYET.

Although I did not invent the game, I did write this implementation from scratch (using Turbo Pascal Version 4.0). I did it mainly for the hell of it, but I improved on the original where I thought it needed it. The two main improvements are the ability to run on monochrome screens (although it looks better in color) and a more responsive feel. I also used the movement keys that are used in the commercial version of the game, although I personally prefer the original movement keys. (In fact, you can use the original movement keys as well; i.e., to move left, 7 or J; to rotate, 8 or K; to move right, 9 or L; to peek ahead, 1 or M; to drop, 4 or Space Bar.) Finally, my version should work at the same speed no matter how fast your processor is; I have heard that that is a problem with the commercial version.

Indeed, Nyet is a very good game. It is completely independent of processor speed; it doesn't break any records, but with 30k (including documentation) is reasonably small; and it is well playable even on a monochrome screen.