Collected here are a few diagrams which make use of The Geometry Applet .

deCasteljau's method of evaluating cubic Bezier curves is a nice example of a diagram which begs for animation.

Euclid's Elements Book VI Proposition 9 has generated some interesting mathematics at the Junior High level. A novel method to divide a line segment, and an interesting construction related to the Fibonacci series were both produced by 13yo David Sloan. The key to proving the correctness of these two constructions is a tiny theorem about ratios.