slackbuilds/desktop/xfce4-embed-plugin

This plugin enables the embedding of arbitrary application windows
into the Xfce panel. The window is resized into the panel space
available, and the associated program can be automatically launched if
it is not open.

Example uses include embedding an instant messaging buddy list, a mail
client's new mail ticker, a simple media application, or a fancy clock
or timer.  Combining with Xfce's ability to auto-hide panels can make
this very convenient