notification-daemon 3.20.0-2 (amd64 binary) in ubuntu bionic

 notification-daemon displays passive pop-up notifications, as per
 the Desktop Notifications Specification.
 .
 The Desktop Notifications Specification 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.