The Horrible National Sport of Chinese People - they called it
"Dry Swimming".
I never play mahjong, but I have a lot of friends who're addicted to it.
Mahjong is international (Taiwan, Japan, China and U.S.). Basic rules are the same, but minor rules can be different from one region to another.
When my friends couldn't get four people to play, they play with the computer. I think you can play it alone with the computer, but I don't play so I don't know whether it's a free online game or a software...