What is a MetroWindow?

The default MetroWindow is made up of following components:
1.Title bar
2.WindowCommand
3.Resize Grip 
4.Window icon

WindowCommand
You can add your own controls to LeftWindowsCommands or RightWindowsCommands - by default, buttons have a style automatically applied to them to make them fit in with the rest of the WindowsCommands. As of 0.9, you are no longer limited to just buttons, but any control. Be aware, you’re responsible for styling anything other than buttons.

To know more about MetroWindow 
visit  https://mahapps.com/guides/quick-start.html