WPF Allows for transparent windows which can help shape our desktop program to anything we can drew. In a few simple steps we can make a triangular program window. Here is how:

In the main application window, set two values: 

Background="Transparent" AllowsTransparency="True"

Use XAML to draw whatever shape you want your window to be. In our case I chose a triangle surrounded by an ellipse

<Ellipse StrokeThickness="3" Stroke="#FF8F0000" />
        <Polygon
    Points="0,200 800,0 800,400"
    Stroke="Purple" 
    StrokeThickness="2" MouseLeftButtonDown="Polygon_MouseLeftButtonDown">
            <Polygon.Fill>
                <SolidColorBrush Color="Blue" Opacity="0.4"/>
            </Polygon.Fill>
        </Polygon>

All that is left now is to capture and handle MouseLeftButtonDown in order to help drag the window arround the screen.

private void Polygon_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  DragMove();
}

The finished window looks like this:

This looks and feels great and can really enhance user experience.