The main set of rules for chess are set by the World Chess Federation - FIDE. Other national and local groups may make slight modifications to the rules. Usually the major differences between rules are about timekeeping or types of draws allowed - the basic game and piece movement are the same. Knights supports standard chess and has some timing flexibility.
There are many variants to standard chess. One source has found over 2000 different variants of the game. Major variants include Fischer Random, Bughouse, Crazyhouse and Suicide. Variants have differing rules on piece capture, piece movement, ending the game and returning pieces to play. Knights does not support chess variants.
Complete rules of standard chess can be found at:
Rules and general chess information can be found at: