There is a way of sending messages to Growl running on a Mac OS X machine from any Unix machine with the standard X11 tools. You do not need to install anything on the Unix machine, just use the xkbbell command.
In short, you need to first install growlnotify on the Mac. You then need a configuration file, xkbevd.cf, with the following content:
Bell() shell "/usr/local/bin/growlnotify --message \"$(name)\" --appIcon X11; true "
Start the X11 server, then start the xkbevd daemon (again on the Mac) pointing to the configuration file you just created (xkbevd -cfg xkbevd.cf -bg). You can then call the command xkbbell on the Unix machine to generate a Growl notification on the Mac. For example, xkbbell "lasers offline". There are detailed instructions and notes on my blog, for those who'd like more information on how this works.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090812044415524