Some Comparisons of Sign Tools
Differences Between Netscape Object Signing and JDK 1.1.x javakey
Netscape Object Signing only works within Communicator. JDK 1.1 signed applets can work in any browser, but with Java Plug-In for the applet to leave the sandbox.<APPLET> tag must be changed by HTMLConverter for plugin use.
JDK 1.1 javakey-signed applets that are trusted get complete access to the host while Netscape Object Signing prompts for specific actions.
JDK 1.1 users can generate their own certificates without needing a certificate authority.
IN general, javakey is less useful than the others.