Opdoku is a free puzzle game available on iPhone that offers a unique twist on Sudoku. With no ads or in-app purchases, it provides a simple and user-friendly interface. The game challenges players to adhere to two key rules: ensuring each digit appears only once in each row and column, and meeting mathematical operations and results within specific groups.

Similar to Mathdoku, Opdoku introduces enhancements that add complexity and variety to the gameplay. Players can opt for puzzles with additional operations like minimum and maximum, solve groups without knowing the specific operation, and tackle puzzles with unknown group results for an extra challenge. With automatically generated puzzles, Opdoku offers a wide range of difficulty levels, from easy 3x3 grids to highly challenging 6x6 grids.