Classical Western chess transferred to a hexagonal board with as few changes as possible. See the page http://www.math.bas.bg/~iad/tyalie/shegra/shegrax.html for more.
 
This version of hexagonal chess was invented in 1939 and registered in 1956 by the Soviet geologist Isaak Grigor'evich Shafran. It was demonstrated at the Worldwide Chess Exhibition in Leipzig in 1960.