Hitori (BrainBashers)

Hitori is a shading puzzle: rather than writing numbers in, you take them out. The grid begins full, with many numbers repeated along rows and columns. You mark squares black to eliminate duplicates until every row and column shows each number at most once. Two rules keep it honest: black squares may not touch each other horizontally or vertically (diagonal contact is fine), and the remaining white squares must all connect into one area.

BrainBashers, run by Kevin Stone, posts Hitori grids at 5x5, 6x6, 7x7, 8x8 and 9x9 every day, each at Easy and Medium, plus a 12x12 weekly special. Each puzzle sits on its own dated page with check, answer, print and restart buttons, an option to show mistakes when checking and an optional clock, and the help page has a walkthrough of a full solve.

The set changes at midnight GMT or at the time zone you choose, the date list keeps the last four weeks, and Random buttons deal extra grids at easy, medium or hard. The site has no adverts and no account.

It suits players who like logic with no arithmetic at all, and the connectivity rule gives the larger grids a satisfying endgame.