Tetris.com offers a free online Tetris game that does not require any additional downloads. Another site that offers a free Tetris game as a tribute to the classic Tetris game is Tetris24.com.
To access the Tetris game on Tetris.com, click on the Play Tetris button to the top right of the screen. The game automatically loads after the redirect, so you are able to play immediately. This site was developed by the official Tetris company, so the game play is exactly like the original version.
Visit Tetris24.com for a flash version of Tetris. The game is located on the main screen, allowing you to play without the need to navigate the site. This is a version developed by fans, so it does not play exactly the same as the original. However, there is a high score status listing that allows players to compete with their own scores.