Lights Out — free browser game

Switch off every light on a 5×5 board. The board starts in a random but solvable pattern. Tapping or clicking a cell toggles that cell and its four orthogonal neighbours (up, down, left, right — never diagonals); edge cells naturally have fewer neighbours, so those toggles affect fewer lights. The instant every light is off you win; your move count is saved, and beating it lowers your best score. Press R or Restart for a new puzzle. Strategy: tapping the same cell twice cancels the move, so be deliberate. Experienced solvers use the 'chase the lights' technique — solve the top row directly, then in each next row press the cells directly below any lights still on in the row above. Repeat down to the last row; if that ends in a known stuck pattern you adjust the first row with a small fixed table.