Find all Enabled Servers in Active Directory that have checked in within a certain timeframe

Get-ActiveADServers.ps1

#Requires -module ActiveDirectory
function Get-ActiveADServers {
    param(
        [String]$SearchBase,
        [String]$Server,
        [PSCredential]$Credential,
        [DateTime]$After = (get-date).AddMonths(-1)
    )
    $GetADComputerParams = @{
        Filter     = {
            enabled -eq $true -and 
            operatingsystem -like '*server*' -and 
            lastlogondate -gt $After
        }
        SearchBase = $SearchBase
        Property   = 'lastLogonDate', 'operatingsystem'
        Credential = $Credential
    }
    ('SearchBase','Server','Credential').foreach{
        $optionalValue = (Get-Variable $PSItem -ErrorAction SilentlyContinue -ValueOnly)
        if ($optionalValue) {$GetADComputerParams.$PSItem = $OptionalValue}
    }
    Get-AdComputer @GetAdComputerParams |
        Select lastlogondate, operatingsystem, dnshostname, distinguishedname
}