When a work has an excellent premise, it's always interesting to find variations on the theme. Haydn knew it. Beethoven knew it. Now Conceptis gets on board with another in their popular series of browser versions of pen-and-paper puzzles, and this time the focus is on perhaps the most popular remix of that ongoing phenom, Sudoku. Chain Sudoku Light Volume 1, designed with the same care as its fellow works, is a twisty variant that's very, very good.