If you are running Ubuntu on your desktop, you certainly have seen the ephemeral balloons that pop-up with notifications. These are designed to make you aware of something, e.g. that you have email, without interrupting your work with a window that you must close.
These balloons, also called bubbles, are shown by a notification daemon, that receives messages from other programs, queue them and presents them in a overlay for a short period of time. On Ubuntu (from 9.04) the notification daemon is called Notify OSD.
Many GUI programs use this desktop notification service to provide unobtrusive information about progress, events and such things. Wouldn't it be nice if you could send such messages from your own Bash scripts? Well, you can with notify-send.
