Tetris

Tetris (Russian: Тетрис) is a falling-blocks puzzle game, released on a large spectrum of platforms. Alexey Pajitnov originally designed and programmed the game in 1984, while working for the Dorodnicyn Computing Centre of the Academy of Science of the USSR in Moscow. Pajitnov has cited pentominoes as a source of inspiration for the game. He derived its name from the Greek numerical prefix "tetra-", as all of the pieces contain four segments, and tennis, Pajitnov's favorite sport.

The game (or one of its many variants) is available for every Nintendo console, as well as other consoles and computer operating system, as well as on devices such as graphing calculators, mobile phones, portable media players, and PDAs. Tetris has even appeared as part of an art exhibition on the side of Brown University's 14-story Sciences Library. Tetris consistently appears on lists of the greatest video games of all time. While versions of Tetris were sold for a range of 1980s home computer platforms, it was the hugely successful handheld version for the Nintendo Game Boy launched in 1989 that established the reputation of the game as one of the most popular ever.

Gameplay
A pseudorandom sequence of tetrominoes (sometimes called "tetrads" in older versions) - shapes composed of four square blocks each - fall down the playing field. The object of the game is to manipulate these tetrominoes, by moving each one sideways and rotating it by 90 degree units, with the aim of creating a horizontal line of blocks without gaps. When such a line is created, it disappears, and the blocks above (if any) fall. As the game progresses, the tetrominoes fall faster, and the game ends when the player "tops out", that is, when the stack of tetrominoes reaches the top of the playing field and no new tetrominoes are able to enter. (The exact definition of a top-out varies from version to version.)

Tetris game manuals refer to the seven one-sided tetrominoes in Tetris as I, J, L, O, S, T, and Z, but players sometimes use other names for the pieces. All are capable of single and double clears. I, J, and L are able to clear triples. Only the I tetromino has the capacity to clear four lines simultaneously, and this is referred to as a "tetris." (This may vary depending on the rotation and compensation rules of each specific Tetris implementation. For instance, in the Tetris Worlds type rules (see below) used in many recent implementations, certain rare situations allow T, S and Z to 'snap' into tight spots, clearing triples.)

Scoring
The scoring formula for the majority of Tetris products is built on the idea that more difficult line clears should be awarded more points. Nintendo's implementations on the NES, Game Boy, and SNES use what is probably the most widely recognized system.

Nearly all Tetris games allow the player to press a button to increase the speed of the current piece's descent, rather than waiting for it to fall. If the player can stop the increased speed before the piece reaches the floor by letting go of the button, this is a "soft drop"; otherwise, it is a "hard drop".

Many games award a number of points based on the height the piece fell before locking. If a piece is manually dropped x lines and locked, these versions will typically award points proportional to the number of lines that the player accelerated the piece. If a piece is not accelerated at all the player will gain no points for that piece unless a line is made.