Cinderella is written in Java, so will run on almost any platform.
It can also be used to put interactive figures on the web easily.

For a nice example of how Cinderella can be used to create
interactive exercises, have a look at June Lester's
Triangle Explorations.
Anyone wanting to put exercises on the Web
should study the source of this page.

The program is good on conics - it has poles and polars built in.
I have produced a few examples, mainly illustrating duality.

Note When you load a page involving Cinderella, it may take
a minute or to to start the applet. When you load subsequent
Cinderella pages, it should be almost instantaneous.