DTET

DTET was a fan game created in Japan with the goal to create the author's own vision of Tetris, different from both the guidelines or TGM. It implements many rule elements that are not seen elsewhere, such as symmetric wall kick (elaborate?), double rotation, a huge number of previews, and on-demand ARE canceling (No line clear delay in ADVANCE or FINAL level).

The game's control system consists of 2 rotate buttons, unlike many other Japanese games which feature a duplicate button for one of the directions (usually anti-clockwise). This potential drawback is overcome as follows: When a piece is rotated, and the other rotate button is presssed while the first button is still down, the piece rotates an extra turn in the direction of the first button, for an overall 180 degree rotation, otherwise known as a "double rotation".

Links
Official DTET Website