The rules of chess have remained pretty much unchanged since the game was invented by the Persians over a thousand years ago. They have also remained pretty consistent, the game having been stable for hundreds of years now. But many variants of the game have also been developed, using changes in the rules, board, the number and types of pieces, and their capabilities. These are collectively referred to as “fairy chess”.

Chess is very popular in Spanish America (Cuba even had a world champion, Jose Capablanca, from 1921 to 1927). When I lived in Puerto Rico, I had the privilege of competing in the Puerto Rico National Tournament, where I was eliminated in the second round by a kid ten years my junior.

There is a form of fairy chess that is also very popular on that island, called ajedrez moderna (Modern Chess). Boards and pieces were available in the stores, and there were clubs and competitions devoted to it, and there is even an extensive literature on strategy and tactics.This is not to be confused with the more inclusive term of “modern chess”, or Nimzovich’s “hypermodern chess” which refers to styles of traditional chess play that have become popular over the last century and a half. Yes, even though official tournament chess rules have not changed in centuries, there are different styles and schools of the game, both regionally and historically.

Ajedrez moderna is similar to traditional chess, its rules being almost identical to the latter, but it is played on a 9×9 board and features extra pieces, the Prime Minister and its associated pawn. The PM combines the moves of Bishop and Knight. Just thought you might be interested…

http://www.chessvariants.org/large.dir/modern.html