Sudokio

Sudokio is a clean and addictive way to play Sudoku online. Start playing immediately without an account, and create one later to save your progress. Every game earns XP, so you level up and can follow your improvement over time. Five difficulty levels run from Easy to Master, keyboard shortcuts let you play efficiently, and a complete history records all your games and times. A leaderboard lets you compare yourself with other players, all inside a minimalist interface that keeps the focus on the puzzle.