You can play with your friends to know there reaction time. This is very simple game in this 10 LED's are moving in a random fashion. And you have to hit a particular LED given by your opponent and you will get four chances to hit the right target. And if he or she hit the target correctly 10 points will be given. So at last the person who has scored more points will be declared as winner.
Advantage of this circuit is that it will not harm the eyes of children when they play for long duration. As instead of video screen this circuit uses LED for display. It can be easily assembled because of less and easily available components. This circuit also produces a sound when you hit the target like you get in video games. So you will get feel of real video game. You can easily power the circuit with the help of adapter available in market.