Good Old Tetris - Play Tetris Online. The game that will never get old.
Word Tetris - Tetris with words
Blockinger - An open source Tetris clone for Android.
Tetris Online Poland - Tetris Online Poland (TOP) is an online tetris game where you can play tetris with your friends and tetris experts from all over the world.
NullpoMino - NullpoMino is an open-source action puzzle game that works on the Java platform.
Tetris on a plane - Simple, open-source HTML/JS/CSS version of Tetris built as an exercise.