See for example [2] which is a post from a Xfce developer on why XFCE had to drop support for the BSD's. It seems like you can run XFCE on BSD, but some featur

See for example [2] which is a post from a Xfce developer on why XFCE had to drop support for the BSD's. It seems like you can run XFCE on BSD, but some features are not supported.. That said, their about page isn't entirely honest, it should mention what features are Linux-only.