An example Java applet
Check out the voodoo doll applet (http://www.virtual-design.com/demos/voodoodoll/voodoo.asp?section=demo&subsection=voodoo).
It is used principly to control and monitor states of the client's browser
It is less evenly implemented than Java, supporting many functions in Netscape 3.0 that are not available in Netscape 2.0 and Inet Explorer
The scripts are loaded, in most cases, with the html file itself, and so it is readily readible by viewing sources.