Hexologic is currently available for free (instead of €4.99) for Linux on Steam.

The game is a Sudoku-like logic puzzle on hexagonal grids, where the dots inside the hexes must be combined so their sum matches the value at the edge. It was developed by MythicOwl.

A Sudoku-like gameplay is taken to a whole new level! ! Immerse yourself in the beautiful world of Hexologic. Solve challenging, yet rewarding puzzles, listen to relaxing music, dive deep into the game’s atmosphere and fall in love in with Sudoku again!

• Relaxation, putting your mind at ease in the immersive atmosphere
• 6 completely different game worlds, each with unique gameplay mechanics
• Over 90 levels designed down to the smallest details
• Well-balanced puzzles
• An atmospheric soundtrack accentuating the game’s ambience

Source: Steam