A theorem of Archimedes on a circle can be generalized to a hyperbola as shown here.
CE is a diameter of the hyperbola. FG is parallel to the tangent at C. H is the intersection of the tangents at F and C.
Observe that EH bisects FG.
The hyperbola has foci A and B.
The family of circles whose center C lies on the hyperbola and which pass through the fixed point D defines an envelope curve.
What does this envelope look like when D lies on A or B?
This app allows you to experiment with an alternate construction of a hyperbola. The tracing of the perpendicular bisector of the segment between a point on a circle and a point outside the circle create a hyperbolic locus. (G-GPE 3)
This app allows you to experiment with the definition of a hyperbola as the set of points in which the difference of the distances from two fixed points is a constant. (G-GPE 3)
The polar line is the locus of the intersections of tangent lines at the ends of chords of teh parabola through a fixed point.
Turns out to be conceptually important - not just a curiosity.
I saw a demo where a foam cube had a knitting needle inserted along the long diagonal, and was rotated by spinning the needle between the palms of the hands.
The sides of the cube formed a curve... in fact a portion of a hyperbola, as this video illustrates.