Author: mrw
Shade some cells so that each region is either fully unshaded or contains exactly four shaded cells that form an L, I, T or S tetromino. Two tetrominoes of the same type shouldn't share an edge. All shaded cells should form a single connected area. No 2×2 group of cells can be entirely shaded or entirely unshaded.
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.