Number puzzles are a Christmas favourite, for whiling away the enforced downtime while family get on with watching Home Alone or similar. Yes, you can resort to a paper puzzle book, but why not go high-tech with a game like Kakurasu?

From the Store description:

Welcome in KAKURASU world, a place where uncluttered tile-based design is dedicated to challenging and addictive gameplay. With only mental arithmetic and deduction for weapons, master these lovely crafted puzzles. In KAKURASU world, all is about properly filling a board to satisfy given targets.

Start your journey with easy-peasy levels then sharpen your mind facing thorny ones and so called hidden mode…

Funny achievement system rewards your progression and keeps you focused on training your brain. 

Here's Kakurasu in action:

No, not part of the game - this is the main menu! You'll work out most of it - I can't decide if this is absolute genius or a usability disaster... it's certainly very different!

There's a graphical and interactive(!) help system, leading you through what to do in solving the number puzzles. Nicely done.

The layouts and levels change, but in this one you're working out which combinations of numbered squares can cause the row and column totals to all match their targets.

You can grab this for free here in the Store. It's very much in the Sudoku vein but simpler - and yet harder at the same time. Nicely programmed on Windows too. The '$' menu function is just for donating - you may wish to send the developer a virtual beer or three?