A great (sadly no longer updated) site about mahjong in Singapore.

The OG site for Singapore Mahjong. Features a playable game too!

Great article on basic rules, hands & odds of getting the various hands.

A good and thorough explanation of Singapore mahjong scoring rules.

A good visual guide to various forms of scoring - Sichuan Bloody Rules, MCR, Riichi

A set of rules commonly played for Forum games

Has a good overview of many types of mahjong playing styles, from around the world.

Has a good overview of many types of mahjong playing styles, with pictorial guides in downloadable format.

English translation of China Mahjong Competition Rules courtesy of Singapore Sparrows Mahjong Network

Good guide to the 81 scoring hands for MCR.