RHQ has the ability to invoke operations on any resource when it triggers alerts. When you combine this with the ability of the Script plugin to run remote scripts via its "Execute" operation, you have a very powerful mechanism to integrate your own processes and rules to help correct or workaround abnormal conditions that occur in your managed environment.
Because I've heard several people ask if RHQ has this ability, I put together a flash demo that shows how you do it. The demo shows how you can execute any script on a remote machine when an alert is triggered by RHQ. For example, if you set up an alert that detects when your app server is using an abnormally large number of threads (a possible indication of heavy load), you can have RHQ execute a custom script on your app server machine to help alleviate problems that might occur due to that condition (such a script could be one that reconfigures a load balancer to help redirect load away from your app server).
The use-cases for this feature are virtually endless. Any set of alert conditions on any managed resource can trigger the execution of any script you have. And as the demo illustrates, it is really easy to set this up within RHQ.