Vial

What it is

A water sort puzzle that tries to be the version of the genre that respects you. No ads, no timers, no lives, nothing to buy. Undo as much as you like. Hints are free and tell you whether a board is still winnable.

Every level is checked before it ships

A solver proves each one solvable from its starting position, so you are never handed a board that was dead before you touched it.

Difficulty is measured, not guessed

Every level is played thousands of times by a simulated player before it reaches you, and its difficulty is that player’s failure rate. The levels the campaign uses are measured again, far more carefully, because ordering two levels whose difficulty differs by less than the measurement’s own error is not ordering them at all.

It collects nothing

No account, no sign-in, and no network access — the released app does not hold Android’s internet permission, so it cannot open a connection even if it tried. The policy says so at greater length.