This is a 3D Chess variant played upon two bisecting boards. Both the horizontal and vertical 'Z' board cross at the King's file, that would be e1-e8 alphanumerically.
 
All standard rules of Chess apply, including castling and en passant.
 
Castling can be preformed to both the horizontal and vertical boards.
 
Pieces can only move from one board to the other from the King's file. So the Pawn on the King's file can capture to both boards.
 
 
Z-Axial Chess was developed by L. Lynn Smith from an idea which was touched upon within the 3D Chess Group at http://groups.yahoo.com/group/3-d-chess