It's a panel plugin to attach x11-plugins/wm* ones into the panel area..., not all of the plugins work but that's expected, most do
+ 26 Aug 2009; Jeremy Olexa <darkside@gentoo.org> + xfce4-wmdock-plugin-0.3.2.ebuild: + amd64 stable, bug 282654 and update HOMPAGE and Manifest, it got broken in the rename.
x86 stable, closing