Geometry applet
David E Joyce of the Clarke University has provided a set of Java classes that allow complex geometrical constructions too be built using parameters passed to a Java applet.
The geometry applet looks as if it could be used to provide dynamic graphics to help students explore locii and circle theorems without the rather imposing deductive framework of the Elements. Watch out for some examples here. You can download the Java class files as Geometry.zip. Look at the HTML code for the Geometry Applet page for examples of how to get the applet funtioning.