Tap: ✕ → queen → clear. Long-press, right-click or drag to mark ✕. Arrow keys + Enter / X / Q work too.
How to play
Place one queen in every row, every column and every colored region. Queens may not touch each other, not even diagonally. Tap a cell once for an ✕ (a note that no queen goes there), again for a queen, and a third time to clear it.