Author: Andrey Bogdanov
Shade some cells so that no two shaded cells are adjacent and the unshaded cells form one orthogonally connected group. No 2×2 group of cells may be entirely unshaded. Some cells are already shaded, and the numbers in those cells indicate the number of shaded cells in the same diagonally connected group as the cell, including the cell itself.
Grid control: Click the mouse button at the selected cell to change the color of the cell. Second click will put auxiliary cross, 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.