TopMenu developer has added a new plugin, which allows using TopMenu under Xfce (Xfce Panel).
Source: Webup8: TopMenu On WebUp8
Like Mac and Unity uses, Topmenu saves space by placing Global on the Task panel.
You can install TopMenu by running the following commands via your systems Terminal
sudo add-apt-repository ppa:webupd8team/mate
sudo apt-get update
sudo apt-get install xfce4-topmenu-plugin
Once installed open the panel preferences and add TopMenu.
Finally you can then move the TopMenu anywhere you prefer.
That's all please enjoy this awesome Menu.