I'm surprised no one pointed out Growl. There's GNotify for linux but it's nowhere near as polished. And in the growl package, there's an extra called growlno

I'm surprised no one pointed out Growl. There's GNotify for linux but it's nowhere near as polished. And in the growl package, there's an extra called growlnotify, which lets you pipe data from processes and show the output in growl form. I use this extensively.