Twindoku: Logic Game

Every square is a sun or a moon. Every level can be reasoned out.

twindoku is a logic puzzle game with no luck in it. You fill a grid with two symbols until the board satisfies every rule the level lists -- and the rules are all on screen, every time. Two taps to learn, and the thinking never stops changing.

WHY IT NEVER FEELS UNFAIR
Each level has exactly one valid answer. At any moment in a solve, at least one square can be proven from the rules already in front of you, so you never guess and never have to back out of a wrong branch. The locked cells you get at the start are your first foothold -- work outward from there. Stuck just means the next certain move is on the board and you haven't spotted it yet.

THE TWO RULES YOU START WITH

Balance: every row and every column holds as many suns as moons. Three and three on a 6x6 grid, four and four on 8x8.
No three in a row: never three of the same symbol side by side, across or down. Diagonals do not count.
That is the whole entry price. Tap an empty square, a small picker opens right there, choose your symbol, tap again to switch it.

THREE MOVES THAT CRACK ALMOST ANY GRID

Find the row or column that is nearly full. Once its suns are all placed, every remaining square in that line is a moon.
Find two identical neighbors. The squares on both ends of the pair are locked to the other symbol.
Read a sun, a gap, then a sun. The cell in the middle can only be a moon.
SIX WAYS THE BOARD GETS DEEPER
From level 3 on, each puzzle stacks one or two extra rules over the basics, so a small grid keeps producing fresh logic:

Equal and cross markers between two neighboring cells: the pair must match, or must be opposite.
Color regions: the board splits into colored areas, and each area needs its own suns and moons balanced.
Blocked cells: marked squares that cannot be filled and do not count toward their row or column. A blocked cell also breaks a run, so the symbols on either side of it are not "in a row".
Edge numbers: a number outside a line tells you which cell holds the first sun of that line, counting from the left edge for a row, or from above for a column.
Junction numbers: a number sitting where four cells meet counts the suns inside that 2x2 block. A 0 or a 4 settles all four cells at once.
Grids that are not square: diamonds, fat crosses, hearts, bow ties, octagons, window frames. Everything outside the outline is background -- not tappable, not counted. Same rules, a different shape to read.
HINTS THAT SHOW THE REASONING
The hint tool does not just fill a square. It finds a cell that can be proven right now, highlights it, and spells out the deduction -- which rule, and what on the board makes it certain ("this row already has all of its suns, so this cell is a moon"). You read it, then press Apply to lock the square in. You come away with the technique, not just the answer.

THREE HEARTS, AND NO DEAD END
A level starts with three hearts. A wrong symbol costs one and tells you which rule it broke, so a mistake is still information. Out of hearts, you can revive -- hearts back, your last move undone, board intact -- or restart the level clean. Nothing ever locks you out of a puzzle; you can stay with a grid until it cracks.

Ten minutes a day is enough to keep your deduction sharp. Brain training that is actually a game: everything you need to reason with is on the screen, and the only other thing required is a clear head.

GOOD FIT IF YOU LIKE
Sudoku, Binairo, Takuzu, Binoxxo, binary puzzles, Nonogram, Kakuro, and any brain teaser you finish by reasoning instead of luck.

Fill every square, satisfy every rule, and the grid solves itself. A pure logic puzzle, one sun and one moon at a time.