Prolly one the best ways to play Riichi Mahjong with AI opponents. It lets you play without being forced to make fast moves and allows you to really think about your hand. It has a handbook that you can pull up at any point to check which yakus you might want to aim for, so all in all a good tool to learn how to play the game. My only complaint is that there doesn't seem to be a way to program keyboard controls and you have to manually click the ignore button for chis and pon a lot, but i still enjoy playing it non the less.

Before this i used to play a flash game that did the same thing (and it's still a good page if all you wanted to do is look up the different hands to reference), but sadly it died when the flash player did so this is a nice alternative for it that and i play from time to time when i have nothing to do and want to play something quick that involves some brain power.

Not really the best for online though, If you wanted to play online against other people then Mahjong Soul is better, that said humans player in that game all tend to go for the fastest and cheapest hands all the time so you really have no time to go for anything decent (yes i'm salty lol). Otherwise online Tenhou is best if you want to play against people that admitantly leave all the time, but at least stay to try for better hands.