The Xfce Notify Daemon (xfce4-notifyd for short) is a smallish program that implements the “server-side” portion of the Freedesktop desktop notifications specification. Applications that wish to pop up a notification bubble in a standard way can implicitly make use of xfce4-notifyd to do so by sending standard messages over D-Bus using the org.freedesktop.Notifications interface.
Additionally, we recommend use with a compositing manager running; in that case Xfce4-notifyd will look a bit nicer and will be semi-transparent and will fade out. This is not required by any means, of course.
Run xfce4-notifyd-config to display the settings dialog. There aren't any other tunables; if you do not see it in the settings dialog, it's not changeable.
Xfce4-notifyd uses GTK+'s standard theming system. You can create new themes by creating a normal gtkrc file. See the example included themes for details of how to reference the various widgets present in a normal notification dialog. You will want to put your gtkrc file in $HOME/.themes/THEMENAME/xfce-notify-4.0 and then start up the configuration dialog to set the theme.
If you think you came up with a cool theme, feel free to attach them to an enhancement request our bugzilla, and we will be happy to include it in the next release. For themes shipped with xfce4-notifyd, we require all parts of them to be distributable under the terms of a license compatible with the GPLv2.
We advise you to use your distribution's package. If you know what you are doing, you can build Xfce4-notifyd from the source package below.