DROD: Journey to Rooted Hold 2.0Free
The Mathematics Association of America called DROD: Journey to Rooted Hold The Best Puzzle Game of All Time. To call it a puzzle game is inadequate, however; the DROD (Deadly Rooms of Death) games are sui generis. They're dungeon crawls for thinkers. Each room (more than 300 in the full game) is a puzzle, and you must plan every action your character takes carefully to ensure that you solve the puzzle and escape the room alive.
And the puzzles have been refined and polished over time by an active community of enthusiastic fans for years. You won't find the graphic glitz of big-publisher games here but you will find utterly unique and compelling gameplay.