Fan game

In the context of Tetris, fan games are computer tetromino games unconnected with Elorg, The Tetris Company, or any other licensor of rights in the Tetris trademark. They tend to follow the well-known rules of Tetris but may not strictly follow any official guidelines.

Straight tetromino games
The following games more or less faithfully replicate the rules of some version of Tetris, either pre-Guideline or post-Guideline:
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 * Aint - free software for MS-DOS, possibly the first copylefted tetromino game
 * Bastet - Literally, Bastard Tetris. Made to be as annoying and frustrating as possible.
 * Bedter by Andrew Bednarz - freeware for Windows and Linux, famously targeted by TTC which alleged "look and feel" copyright violation
 * Breakris by Jürgen Müller - freeware for Windows. It has a very good single and multiplayer-Tetris, plus Breakris - Breakout and Tetris at the same time.
 * Cultris
 * GinT - Falling Tetromino game within the 3D world of Second Life.
 * Heboris
 * Lockjaw: The Overdose (formerly Tetanus On Drugs) - free software for Game Boy Advance, inspired by Tetripz and considered by many players to be superior in look and feel to the GBA version of Tetris Worlds
 * Tetripz by Mute Fantasies - freeware for MS-DOS, with visual distortions of the playfield
 * Tetris Weightlifting - A modified version of Tetris using exercise equipment as the control mechanism.
 * Blocks A Java version of the game.

Variants
These games have game play rules inspired by Tetris, such as rotation of shapes to form complete lines, but introduce rule variations that change the game play greatly.
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 * 3DTRIS - 3dtris.de A clone of Blockout (3D variant of Tetris) in Macromedia Flash. Its gameplay is very smooth, just like original Blockout. Online high score list with growing competitions.
 * Quadra - Open source clone with cascade gravity. Features very fast-paced online play.
 * Java Tetris - A Java Tetris game that follows the gameplay rules of the original, but has more than 30 shape types and a few new game modes, including a "Hardcore" mode where the game is played on a 125x125 grid.

Comparison of notable fan games

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