Here is a version using Text::ParseWords and a modified spawn subroutine, which uses exec in scalar context. This allows parameterized command execution. 
#!/usr/bin/perl

use Getopt::Std;
use Text::ParseWords;
my %opt = (n => 1);
getopts('r:n:v', \%opt) or usage();

my $cmd = shift;
@ARGV = shuffle(@ARGV) if $opt{r};

my %pid;
while (@ARGV) {
  if (keys(%pid) < $opt{n}) {
    $pid{spawn($cmd, map { shellwords($_) } shift @ARGV)} = 1;
  } else {
    delete $pid{wait()};
  }
}

1 while wait() >= 0;

sub spawn {
  my $pid = fork;
  die "fork: $!" unless defined $pid;
  return $pid if $pid;
  warn "@_\n" if $opt{v};
  exec qq(@_);
  die "exec: $!";
}

sub usage {
  print STDERR "Usage: $0 [-n N] [-r] [-v] command arg1 arg2...
Run command arg1, command arg2, etc., concurrently.
Run no more than N processes simultaneously (default 1)
    -r: run commands in random order instead of specified order (unimp
+l.)
    -v: verbose mode
";
  exit 1;
}

[download]
The following snippet will ping google.com and amazon.com once in the first chunk and yahoo.com in the second. 
runN -v -n 2 'ping -n 1' google.com amazon.com yahoo.com
ping -n 1 google.com
ping -n 1 amazon.com

Ping google.com [72.14.207.99] mit 32 Bytes Daten:

Antwort von 72.14.207.99: Bytes=32 Zeit=116ms TTL=242

Ping-Statistik für 72.14.207.99:
    Pakete: Gesendet = 1, Empfangen = 1, Verloren = 0 (0% Verlust),
Ca. Zeitangaben in Millisek.:
    Minimum = 116ms, Maximum = 116ms, Mittelwert = 116ms

Ping amazon.com [72.21.210.11] mit 32 Bytes Daten:

ping -n 1 yahoo.com

Ping yahoo.com [66.94.234.13] mit 32 Bytes Daten:

Antwort von 66.94.234.13: Bytes=32 Zeit=185ms TTL=54

Ping-Statistik für 66.94.234.13:
    Pakete: Gesendet = 1, Empfangen = 1, Verloren = 0 (0% Verlust),
Ca. Zeitangaben in Millisek.:
    Minimum = 185ms, Maximum = 185ms, Mittelwert = 185ms
Zeitüberschreitung der Anforderung.

Ping-Statistik für 72.21.210.11:
    Pakete: Gesendet = 1, Empfangen = 0, Verloren = 1 (100% Verlust)

[download]
print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});

In reply to Re^3: Parallelization of heterogenous (runs itself Fortran executables) code by codeacrobat
in thread Parallelization of heterogenous (runs itself Fortran executables) code by Jochen

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