In the applets, the pendulum doesn't appear to change length when the length value of the pendulum is changed. This is only a small point as the physics seems to be correct.
This site currently does not work with Internet Explorer 6.0. The images do not show, and when one uses the "Back" navigation button on the browser, the html source appears rather than the rendered page. In addition, the applets do not run under the MS Java VM with IE 6, although they do work when the Sun 1.4 Java VM is used.
These problems do not occur with IE 5.5 and earlier, Netscape, or Mozilla.