Sixtis

Sixtis is tetris with a very large number of settings and game modes. There is a "sudden mode" in which the pieces fall instantly. In "field without borders" mode, the pieces fly through if they don't get caught on anything. You can choose how big the pieces fall out and edit the field.

There are different complications, such as when supplied rows don't always disappear, or when only a few merged rows disappear at once. You can choose the direction of gravity, for example pieces can fall up, to the right and to the left.