X-Sums is an interesting variation on number games, which sort of works like a mash-up of crossword puzzles and Sudoku. The numbered squares on the grid tell you the total of the tiles below (the number below the slash) and to the right (the number above the slash). It works pretty well and is intuitive once you learn how it works. Mouse control is not offered, but keyboard control is not too clunky. It offers a useful "check" feature which immediately removes any incorrect answers, as well as three different difficulty levels.
9/6/2024