JMX is not a server, it is an API that allows you to monitor (and possible alter) the inner workings of a JVM. That's particularly interesting for servers, because those are long-running and may need to be tweaked without bringing them down. It is very much alive, tools like VisualVM rely on it heavily. It's even part of JSE as the javax.management package.
Not sure what you mean by the comment about Tomcat; what are you looking for that VisualVM doesn't offer?
I'm not interested only in monitoring the JVM. I have my own MBeans which are exposed and I want to access them easily.
Specifically, I'm looking for a WAR file that I can deploy in Tomcat and will simply give me access to my MBeans through a browser (I know that JBoss has that capability).