JADMaker is a simple tool that converts Java JAR files to JAD format, necessary for some mobile devices, in order to play games.
After opening JADMaker, simply browse to the JAR file, click convert and the JAD file will be saved on your desktop. JADMaker is aimed primarily at users of older mobile phones that want to play games and so it won't be necessary for most new phones. The developer site also seems to have disappeared so there is no support if you encounter any problems.
JADMaker is easy to use and converts JAR to JAD in seconds.