Author: Andrey Bogdanov
Place a few chess queens into the grid. Numbers show the number of queens attacking the cell with the number. A queen attacks all cells in the same row, column or diagonal which are not blocked by another queen. Queens can't be placed to cells with numbers.
Grid control: Click the mouse button at the selected cell to set/remove a queen. Second click will put auxiliary cross sign, which doesn't affect correctness of the solution, but helps visually. You can also drag the content of one cell to another with the mouse. More details about grid control are at the help page.