Known clones of Tetris: EGAint 1989, Blockout 1989, Tetris 2 1990, Frac4D 1990, Tetris Max 1993, Quadrapassel ?, KBlocks ?, Wordtris ?, La Bastille 2000, Tetris 1D 2002, Tetris Grand Master 3 2008, NullpoMino 2008, Mino 2009, Not Tetris 2010, Tetraminos 2016. All of these are published without permission and some use the registered trademark "Tetris" without permission. The game Mino is the only game on this list that lost a copyright case to The Tetris Company. "Tetris" is now a commonly used term for a "tetrislike" game, so The Tetris Company can not win a case even for using the exact term. Have you ever heard of a "Roguelike" game? In 1980, an RPG game called "Rogue" was published. Cloning games is not new. Proof of direct copying of assets is what wins IP cases. It was shitty to use the same name, but it isn't illegal. That name is not registered and it is free for anyone to use.