MathemaGrids (BrainBashers)

MathemaGrids is a cross-sum puzzle using all nine digits. The board is a 3x3 grid of empty squares with an operator between each pair, making three sums across and three sums down, each with its answer at the end. You place 1 to 9, each exactly once, so that all six sums are correct.

The twist is the order of operations: there isn't one. Every sum is worked strictly from left to right, or top to bottom, so 2 + 5 x 9 means (2 + 5) x 9 = 63, not 47. The site adds some helpful guarantees: you will never see ÷ 1 or x 1 (though 1 x can appear), and no step of a calculation ever drops below zero or turns into a fraction.

Kevin Stone's BrainBashers posts three of these a day, Puzzles A, B and C, all of a similar difficulty. Each can be opened with 0, 1, 2 or 3 random digits already placed as hints, and the play page also has a hint button, plus check, answer, print and restart, an option to show mistakes and an optional clock. The puzzles change at midnight GMT or at the time zone you set, and a few weeks of earlier days stay in the date list. No adverts, no account.

Beside the daily three, Random buttons at three levels give fresh grids without limit. A solved daily shows your time and the hints you used, with a share button.

It suits anyone who enjoys mental arithmetic and wants a short daily number puzzle.