Classical Western chess transferred to a hexagonal board with as few changes as possible. See the page http://www.chessvariants.com/hexagonal.dir/hexagonal.html for more.
 
This version of hexagonal chess was invented in 1936 by Wladyslaw Glinski. During his life Glinski successfully promoted the game, which attracted hundreds of thousands of players in Eastern Europe; he also saw the creation of an International Hexagonal Chess Federation and several international tournaments. He died in 1990, and the English-speaking world has heard much less of this game since then; but Hungary, Belarus, Ukraine, and Russia appear still to have many active players.
 
The notation used in this Zillions implementation is not Glinski's standard, which does not fit conveniently into the ZRF language. The cells on the Queenside half of the board and on the centerline are labelled correctly, but in the 'official' notation, the cell which here is called g2 should be g1; g3 should be g2; h3 should be h1; i4 should be i1; etc. That is, in the Glinski notation each file bends at the centerline at an angle of 120 degrees.