libnotify and notification-daemon are part of
the galago
project, a "desktop presence framework". libnotify shows
popup windows on your desktop to alert you from some event, like new
mail or an IM. I like the idea of use a single program to manage all
your desktop notifications instead of having to implement the same
code over and over again on all your apps. AFAIK libnotify is
desktop-agnostic so it should work on GNOME, KDE, Xfce, etc.
What about emacs? Well, if you
use jabber.el for
jabber
chatting, erc
or rcirc for
IRC you can use libnotify to do some fancy notifications.
For
erc this
guy hacked the libnotify support. I haven't tested personally
but seems interesting.
For rcirc there's
a wiki
page about rcircNotify
For jabber.el I wrote a libnotify alert, here it is the wiki page for it.