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 * a fixed amount (30 I think), with added points for dropping the piece fast.
The Mega Drive/Genesis version had an interesting bug in it. When holding down the drop button, the block fell at a fixed rate, which didn't change as the game got faster, which meant that it was eventually slower than the normal falling speed.