PowerShell function :: Retrieve list of Group Policy Objects that are not linked to any OU.

GetUnlinkedGPOs.ps1

function Get-UnlinkedGPOs {
    [string[]]$results = @()
    Get-GPO -All | ForEach-Object {
            if ( $_ | Get-GPOReport -ReportType XML | Select-String -NotMatch "<LinksTo>" ) {
                $results += $_.DisplayName
            }
        }
    return $results
}

# Usage:
# foreach ($gpo in Get-UnlinkedGPOs) {
#     Write-Host $gpo
# }