What's a good iOS game for engaging in strategic thinking during downtime, perhaps while waiting for research data to process?

I've recently been exploring 'Domino' by ZiMAD on my iPad, and I find it's a surprisingly elegant way to pass the time between tasks. As someone who appreciates strategic thinking, I find the game's mechanics engaging without being overly taxing. The user interface is clean and intuitive, which is always a plus. It's an interesting implementation of a classic game, and I appreciate that it's available cross-platform, so I can pick up a game on my phone if I'm away from my desk. I can envision using this in a classroom setting, perhaps as a break activity during a long lecture. The ability to play online with others also presents some interesting possibilities for collaborative problem-solving, although that's an area that would require further investigation. Overall, it's a pedagogically sound way to engage the mind during brief periods of downtime.