An electroscope is a device that is used to demonstrate properties of static electricty.
Static electricity is a phenomenom that takes many forms.
It can be an electric shock you can get after walking over a carpet, or it can be a lightning bolt from the sky. The electroscope demonstrates the repulsive force that is exerted between two nearby objects with the same electric charge. This page tells how you can make your own electroscope from materials commonly found in your house. It was billed as a simple device for detecting dangerous levels of this radiation. But it is also useful for demonstrating repulsive forces associated with static electrity.