It is definitely true that one of the things I miss most about Java is its wealth of monitoring tools for running apps. The monitoring console for Java5 is incredible, and gives you realtime insight into how your apps are performing. We've all been waiting around for something similar in the Rails space. I've recently started looking into FiveRuns (http://fiveruns.com), and I'm very impressed. FiveRuns is a management console that spans all your infrastructure components; on our XServe, it is monitoring OSX system level information (basically, everything Apple's System Monitor tracks), two separate MySQL instances and our Apache instance.
From their website, it seems that you can also monitor JVMs, Oracle instances, JBoss, Tomcat, Linux servers, and more. Now, obviously, the thing that intrigued me most about their tour was the tease about being able to monitor Rails apps. Check out this screenshot for the tease. FiveRuns is going to be at the Rails Edge at the end of this month with a "special announcement", so here's hoping that this is the release party for Rails monitoring.
What's almost as cool is the way their app works. The monitoring console is a hosted app that received data dumps from a "Smart Client" you install on your server. All the information is pushed from your servers to their host, so no inbound tunnel is required. This is the same setup as 6th Sense, who does project development tracking through a series of "Agents" installed on developer and test boxes. It is very interesting to see the growth of the "smart agent" technologies for collecting information -- lots of tiny little sensors floating around your systems and reporting back to the mothership. Very Vernor Vinge.