Also known as:
Logi-5, Logi-9, Squiffy
The rules are as per a regular sudoku, except that the normal 3x3 boxes have been replaced by irregular nine-cell shapes. Letters (A-I) sometimes replace digits in this puzzle.
Logi-5 is a smaller version of the same puzzle, using only the letters A to E, and five-cell shapes in a 5x5 grid.