Columns
Columns is a non-tetromino falling block game franchise, developed by Sega as a response to the popularity of Tetris in regions where companies other than Sega had an exclusive Tetris license from Elorg. Many Sega Game Gear handheld systems were bundled with Columns.
Columns uses only the I trimino, where each block is colored with one of a selection of four to six colors represented as different gems. The player can move the piece sideways into a playfield whose width may be 6 or 7 blocks and whose height is variable (12 to 18 blocks depending on version). The pieces cannot be rotated, but the colors within the piece can be rotated. After the piece locks, three or more of the same blocks aligned horizontally, vertically, or diagonally disappear, and the blocks on top fall into place, possibly causing a cascade. The scoring is roughly number of lines of 3 * chain * level+1 * 30, with added points for dropping the piece fast.
The Mega Drive/Genesis version uses as 6x13 playfield, and has fast DAS, lock delay, and some levels that are slower than the previous level. It also has an interesting bug in it. When holding down the drop button, the block falls at a fixed rate, which doesn't change as the game gets faster, which means that it is eventually slower than the normal falling speed. However, unless you can let go of drop before the piece lands, you won't have any lock delay, which may not always be desireable.