Author: O-le_o-le
Shade some empty cells black to create a single connected group. Cells with numbers cannot be shaded, and the shaded cells cannot form a 2×2 square anywhere in the grid. Each numbered cell indicates how many black cells can been "seen" in total looking in the four orthogonal directions until the first white cell or the edge of the grid.
Grid control: Click the mouse button at the selected cell to change the color of the cell. 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.