xfce4-wmdock-plugin
Xfce4-wmdock-plugin is a wm dockapp plugin for the Xfce panel, version 4.14 or higher. It detects dockapps running on the system and swallows them.
Homepage
xfce4-wmdock-plugin source code
Credits
Based on a previous plugin, but updated to work with GTK+ 3 and xfce4-panel-4.14 and newer. Started with the xfce-sample-plugin.