This explorable is not used in any lesson app (yet), but it's such a nice idea, I had to develop a tool for it. Basically, you can use points on two concentric circles to create all the different types of quadrilaterals we typically study in high school. Just give it a go. Click on two points to draw a line segment between them. Connect the line segments to draw a quadrilateral. If you draw a special quadrilateral, the little green control panel tells you what you've drawn.

This tool shows that you can get used to creating quadrilaterals using the properties of their diagonals. The diagonals of quadrilaterals can be: perpendicular or not, bisecting each other or not, congruent or not. So, a square has congruent, perpendicular diagonals that bisect each other. A trapezoid's diagonals are congruent, not perpendicular, and not bisecting.

Go find the others!