Tetris played on a
hexagonal grid with
tetrahexes (groups of four connected
hexagons). There are several existing
shareware/
freeware games based on this
concept, at least two of them called Hextris.
A common design decision in such games is that columns of hexagons can fall past one
another, even though the protruding points of the hexagons would seem to make this
impossible in real life.