Visualizing radians

Sam Shah shared a GeoGebra applet created by a colleage of his which does a beautiful job of demonstrating what a radian is. He wrote about it here. I made minor modifications, mostly so that the word radian doesn't actually appear. Here's that slightly modified version.

Compass and Straightedge Construction Challenges

Ancient Greek Geometry from Nico Disseldorp's Science vs. Magic is a simple but elegant applet which gives compass and straightedge constructions the feel of a game. You start with two points and are given a list of things to construct, along with the number of steps in which you ought to be able to complete each construction. Click on two points and you create a line segment between them. Click one point and drag and you get a circle centered at that point. You score when you complete each construction, and score more when you do it within the number of steps prescribed. The first task is Proposition 1 of Book 1 of Euclid's Elements. The applet works equally well on a tablet or a standard computer.