Birddoku

Birddoku is a logic grid wearing a bird costume. Level one is four by four with four birds to place, and the board is carved into irregular colour regions rather than neat boxes. Three hearts sit in the corner.

One bird per row, one per column, one per colour region, and no two birds touching, not even at a corner. Nothing on screen spells that out, but the board teaches you the rule the moment you break it. A bird placed diagonally beside another turns straight back into a cross and one heart goes dark.

Each square takes two taps. The first leaves a cross, which is how you mark a cell you have already ruled out. The second places a bird. An auto-mark switch in the menu will add those crosses for you, and it starts turned off.

Undo, a pair of hints and a restart button line up beneath the board, while a level picker lets you jump around. The grids grow from here, and that is where the crosses stop being decoration and become the only way you keep track.