Proximity is a classic turn-based strategy Flash game that is somewhat like a cross between Risk and Go. It is surprisingly simple to learn and takes about 5 minutes to play. You can play against the computer, or against a friend at the same computer.
Instead of simply moving one object around the screen to avoid the falling dots, in Formation you must control an entire setup of orbs that rotate and periodically change position. Touch one of the flashing white balls that fall from the top of the screen and it becomes part of your formation, thus forcing you to be mindful of yet another ball's position and causing your brain to hurt.