Nyet

Nyet (Russian for No) is a freeware Tetris clone using ANSI graphics. The following was taken from the game's readme file:

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. 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