$parallelCount = 2
$jobList = New-Object System.Collections.ArrayList
$jobStatus = New-Object System.Collections.ArrayList

$null = $jobList.Add({start-sleep -seconds 10; write-host "10 seconds done"})
$null = $jobList.Add({start-sleep -seconds 20; write-host "20 seconds done"})
$null = $jobList.Add({start-sleep -seconds 30; write-host "30 seconds done"})

Write-Debug "$(get-date): starting jobs"

while ($jobList.Count -gt 0 -or $jobStatus.Count -gt 0) {
    $runCount = $([Math]::Min($parallelCount,$jobList.Count))
    foreach($i in 1..$runCount) {
        if($runCount -gt 0) {
            $j = Start-Job -ScriptBlock $jobList[0]
            $null = $jobStatus.Add($j)
            Write-Debug "$(Get-Date): started job: $($jobList[0])"
            $jobList.Remove($jobList[0])
        }
    }
    $null = Wait-Job -Job $jobStatus -Any
    $completedJob = $jobStatus | ? {$_.State -eq "Completed"} 
    if($completedJob) {
        Receive-Job -Job $completedJob
        $completedJob | % { $jobStatus.Remove($_) }
    }
}