3Doku is a 3D puzzle game -- a sudoku wrapped around a cube. Fit the numbers 1-16 onto each face of the cube, and each 'row' and 'column' -- but rows and columns wrap around the cube to form loops. There are a few ''3D sudoku'' variants, with names like 'sudokube' and 'quboku', but most of them are just 2D sudokus stacked up or placed edge-to-edge (or, in one case, a Rubik's Cube with numbers drawn on). 3Doku is one puzzle on one cube. It might take a minute to wrap your head around it, but once you do it's as simple and elegant as the 2D version (with all the frustrating complexity that brings). Includes a hint system in case you get stuck -- but the hints are based on what you have so far, so if you've already messed up then the hint will just help you get further along the wrong path. The app can generate puzzles in 4 difficulty levels, but has 100 pre-generated ones at each level so that slow devices don't have to wait.