Find out old AC Computers

PowerShell script:

# Gets time stamps for all computers in the domain that have NOT logged in since after specified date

$time = Read-host "Enter a date in format mm/dd/yyyy"
$time = get-date ($time)
$date = get-date ($time) -UFormat %d.%m.%y

# Get all AD computers with lastLogonTimestamp less than our time
Get-ADComputer -Filter {LastLogonTimeStamp -lt $time} -Properties LastLogonTimeStamp |

# Output hostname and lastLogonTimestamp into CSV
select-object Name,@{Name="Stamp"; Expression={[DateTime]::FromFileTime($_.lastLogonTimestamp)}} | export-csv old_users.csv -notypeinformation

Source: http://blog.mattvogt.net/