Free brain games and logic puzzles

You reliably improve at the specific game you practise, and the techniques involved - systematic scanning, chunking, working backwards from constraints - are real transferable skills. But the evidence that brain training raises general intelligence is weak, so the honest answer is that these are excellent mental exercise and enjoyable, not a proven cognitive treatment.

Sudoku at its top difficulty and Minesweeper on the expert board demand the most sustained logic. Lights Out is the most conceptually tricky, because the solution method is not obvious until you learn light chasing.

Sudoku is the standard answer and has a new daily puzzle here, but Minesweeper is arguably a better pure deduction game because every number on the board is information you have to combine.

Yes, all of them, with no account, no download and no time limit on how much you play.