To monitor automated build systems the following XML format has been specified by the vendor of the CruiseControl build system: http://confluence.public.thoughtworks.org/display/CI/Multiple+Project+Summary+Reporting+Standard
Build systems may provide a report using this XML format. Hudson supports this since version 1.154.
Monitoring software signals the state of the jobs on the build system in different ways. Typical is the use of tray icons and balloon popup messages.
In Hudson the URL to this report is http://hudsonserver:port/cc.xml
In theory you can use any monitoring that supports CruiseControl to monitor Hudson too. Here is a small list of tools:
Written in Java: JCCTray (uses SWT; configuration to use: Server Name: "My Buildsystem", Server Type: "CruiseControl", Server URL: "http://hudsonserver/cc.xml?" the trailing question mark must be there!)