$start = Get-Date

$task1 = { Start-Sleep -Seconds 4; Get-Service }
$task2 = { Start-Sleep -Seconds 5; Get-Service }
$task3 = { Start-Sleep -Seconds 3; Get-Service }

# run 2 in separate threads, 1 in the foreground
$thread1 = [PowerShell]::Create()
$job1 = $thread1.AddScript($task1).BeginInvoke()

$thread2 = [PowerShell]::Create()
$job2 = $thread2.AddScript($task2).BeginInvoke()

$result3 = Invoke-Command -ScriptBlock $task3

do { Start-Sleep -Milliseconds 100 } until ($job1.IsCompleted -and $job2.IsCompleted)

$result1 = $thread1.EndInvoke($job1)
$result2 = $thread2.EndInvoke($job2)

$thread1.Runspace.Close()
$thread1.Dispose()

$thread2.Runspace.Close()
$thread2.Dispose()

$end = Get-Date
Write-Host -ForegroundColor Red ($end - $start).TotalSeconds