Appnr

a daemon that displays passive pop-up notifications

The Desktop Notifications framework provides a standard way of doing
passive pop-up notifications on the Linux desktop. These are
designed to notify the user of something without interrupting their
work with a dialog box that they must close. Passive popups can
automatically disappear after a short period of time. as per the
Desktop Notifications spec

http://www.galago-project.org/specs/notification/index.php.