Notes About PowerShell: The Simplest GUI

Create the following script (in PowerShell ISE), and then run it:

# Initialize the PowerShell GUI
Add-Type -AssemblyName System.Windows.Forms
  
# Create a new window form
$MasterFrame = New-Object System.Windows.Forms.Form
  
# Display the form
$MasterFrame.ShowDialog()

That's all there is to creating a GUI window using PowerShell. Here's another rendition, just for comparison:

# Import the GUI pieces
Add-Type -AssemblyName System.Windows.Forms

# Create a new form<
$form_1 = New-Object System.Windows.Forms.Form
  
# Display the form
$form_1.ShowDialog()

For a more complex look, see here.