J2EP is an extensible reverse proxy for Tomcat and other J2EE containers. It’s equivalent in functionality to mod_proxy for Apache; see this article for a description of why you would want to do this.

I’m posting this because I had a devil of a time finding J2EP through Google; this is a good example of where Google’s relevance ranking or query expressiveness falls short. (Lots of articles on how to use Apache as a reverse proxy for Tomcat, which isn’t a help if you want to use Tomcat without Apache.)