Turn on all the lights. Flipping a switch flips that light and its neighbors — above, below, beside, never diagonal. Go from all-off to all-green. In the harder modes each flip cycles through more colors; in Impossible mode, well — see for yourself.
Where this game leads: a 5-minute solution summary, our favorite patterns — solution matrices rendered as art — and the in-depth explainer, where the whole thing turns out to be linear algebra.
Bugs, observations, conjectures, and theorems to [email protected].