Notify-send is included in the package libnotify-bin in Kubuntu. It’s an interesting package that I have to make some use of.
From the man-page:
With notify-send you can sends desktop notifications to the user via a notification daemon from the command line. These notifications can be used to inform the user about an event or display some form of information without getting in the user's way.
It can be used for reporting stuff in the systray, like finished file transfers or other small notifications. It looks exactly like the notification for new mail in KMail.
This example shows the message for 5000 milliseconds, with an icon and a heading:
This is what the result looks like:
Another interesting example of notify-send can be found here.