Fours - Unlimited Mathdoku Puzzles!

What is Fours? Fours puzzles are like Sudoku puzzles with an arithmetic twist. In Fours, each row and column must contain the numbers 1-4 with no repeated values, much like Sudoku. However, the board is broken up into cages, with each cage containing a "target" number and an operation. The values inside of each cage must use themselves, combined with the operator, to make the target number.

In Fours, you can choose to play either random puzzles or Challenges (which involve solving back-to-back puzzles in under a specified time limit). In both modes, you can try to beat your best times, or earn score by solving puzzles under certain time limits.