Microsoft Minecraft is a challenging game which was found to help promote learning based on recent study:

http://www.cnet.com/special-reports/minecraft/mindcraft-helping-students-learn

Microsoft’s popular video game Minecraft helps kids learn everything from programming, science and math to art, languages and history. Concerned because you can’t pry your daughter away from Minecraft? Worried that your son spends every moment obsessing over moves in the super-popular video game?   Chill. It turns out that Minecraft builds up brain cells instead of dissolving them.

Minecraft isn’t about bloody broadswords and burning rubber. It has no complex story lines or gorgeously rendered images of alien soldiers. Instead, it’s filled with people, animals, trees and buildings that look as if they were built from digital Legos. And in a way, they were: The Minecraft universe is made up of blocks representing materials such as dirt, trees, stone, ores and water. Players mine and then use these blocks to craft the shelters, tools and weapons they need to protect themselves against nightly attacks from monsters called “mobs.”

Kids pick up more advanced computer skills through Minecraft’s “command blocks” — code that changes the rules of the game. That can be anything, from altering the weather to generating an invincible flying squid.  “Because there’s no overt goal, no immediate plot, no structure, you have the flexibility and freedom to do what you want,” says Jeff Haynes of Common Sense Media, which rates software and games for age appropriateness and gives Minecraft a top “learning” score. “It fosters life skills like creativity, curiosity, exploration and teamwork.”