This site provides direct interaction with geometric curve-drawing devices, courtesy of Java Sketchpad. If the links below whet your appetite for more information, then check out my book, Exploring Conic Sections with The Geometer's Sketchpad.
Intersecting Circles The Sliding Triangle
The Falling Ladder The Taut String
The Bent Straw The Folded Rectangle
The Folded Circle Van Schooten's Parabola
Van Schooten's Ellipse The Expanding Circle
Congruent Triangles Constant Area Rectangles
Concentric Circles Van Schooten's Hyperbola
Tangent Circles Tangent Circles, Part 2
The Burning Tent Problem Congruent Triangles, Part 2