Tetris Online (Japan)

Tetris Online is an official online Tetris game for Microsoft Windows 2000/XP/Vista. (Early beta versions suffered from problems when running in Vista.)
 * The prices are 300Yen/5days, 950Yen/30days, 1950Yen/90days.Source
 * No ARE, IRS, IHS is present.
 * T-Spin recognition is nearly 3-corner T, but T-Spin with Wall kick displays as "T-Spin Mini". In single player mode, there is no difference to Tetris DS. But in VS modes, "T-Spin Mini" sends fewer garbages than T-Spin (no kick).
 * DAS is very slow and useless.
 * Need rapid left key or rapid right key to shift quickly.
 * Only 2 next pieces are visible for the beta test.
 * The default value of next pieces is 1.
 * At the default value, you can use hold 5 times every games.
 * Randomizer is different from other games. It uses variant of Random Generator. It is regular 7 piece bag + 1 random piece system for the beta test. Source
 * Time Attack, Challenge, Marathon, VS COM, Multi mode is present.
 * Time Attack: Well known 40-lines time attack mode.
 * Challenge: 10-minutes score attack mode. Unlike to the Tetris Zone, game ends immediately if the level timer runs out.
 * Marathon: Standard Tetris mode. Game ends in level 15. Required points to increase a level is much shorter than other guideline compatible games.
 * VS COM: Battle against AI-controlled player. The AI player uses regular 7-piece bag system and 6 previews, so you must fight in unfair situation.
 * Multi: Battle against other players.
 * (Practice): It is not a real game mode, but you can play it in Multi mode. (After you die, or before the game starts) Game continues until the current match ends or the match starts. The gravity becomes 20G in level 18.
 * You can buy some items.
 * Next 30 days: 100Yen: You can see 6 next pieces for 30 days.
 * Hold 30 days: 150Yen: You can hold pieces unlimitedly for 30 days.
 * Garbage Tetris: 200Yen: When you do Tetris on VS COM or Multi mode, you send garbage with 2 gaps in the probability of 10% for 100 games.
 * Garbage REN: 200Yen: When you do REN on VS COM or Multi mode, you send garbage with 2 gaps in the probability of 15% for 100 games.
 * Garbage B2B: 200Yen: When you do Back to Back on VS COM or Multi mode, you send garbage with 2 gaps in the probability of 20% for 100 games.
 * Garbage T-Spin: 200Yen: When you do T-Spin on VS COM or Multi mode, you send garbage with 2 gaps in the probability of 20% for 100 games.
 * Anti-Miss: 100Yen: This item prevents your harddrop misses for 100 games.

Official Site