HackIt! is a strategic game where your goal is to control as many Web sites as you can by hacking them. It is played on an infinite map (the whole Web) where hackers struggle for the control of the Internet. The game involves scanning sites to know who they belong to, hacking your friends' favorite pages, or tracking them to kick them out of the net.
QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.