There are several contenders for the title of weirdest Tetris clone. Zmeyelov stands a good chance of winning.
The original title is a Russian word that has no real English equivalent. A 1985 movie of the same name was distributed in the US under the name Zmeyelov, which is a more or less exact transcription of this word, which denotes a snake catcher or snake hunter. And snakes is what Zmeyelov is all about.
Instead of blocks there are snakes falling down this pit or well. While they are falling, you can manoeuvre them with the cursor keys, and they will behave like the snakes in the well-known arcade games. When a snake hits another of the same color, it replaces the former. Main strategy is therefore to avoid covering one snake completely with others, as happened with the light blue one in the screenshot above.
Zmeyelov is a Russian game, an English version does not exist to my knowledge (the 1996 Windows version had was translated into English as WildSnake). Since there is little text, and what text there is is technically nearly all graphics, this won't be a problem. Only on the title screen there is a line of gibberish on non-Russian DOS versions. The menu items are, from top to bottom: Start, Level, Sound, Credits, and Quit.
This is a demo version that lets you play only for a short while, but it's the only thing you will find at all. Still it's worthwhile just to check out how weird a Tetris clone can get.