Sudoku (Gridgames)

Gridgames, from Gridgames GmbH, is a collection of free logic and word puzzles that runs in the browser and as an Android app, from Arukone and Battleships to GridWords and QuadWords. Its sudoku section offers a new set of puzzles every day.

The rules are classic: fill all 81 cells with the digits 1 to 9 so that each appears exactly once in every row, every column and every 3x3 block. Each day brings a list headed Today's puzzles: seven numbered grids, from an easy No. 1 through two medium and three hard ones to a No. 7, each with its own play button and a slot for your time. Everyone sees the same grids on the same day, and arrows beside the date step back to earlier days.

The player shows a timer, a number pad, and buttons to check the grid and undo moves. Gridgames also has many sudoku variants, such as killer, diagonal, colour and mini sudoku, if you want more after the daily ones.

It is free with no sign-up, and the page can be played in some 25 languages, English and German among them. Display ads sit beside the board on a desktop and above and below it on a phone, without covering the grid. Signing in is only needed to keep statistics and compare them with friends. It suits sudoku players who like to pick their level each day and have a big library of other logic puzzles in the same place.