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