Here's a roll-your-own asynchronous spinner using fork under Win32. It's pretty crude as-is, but could be fairly easily wrapped up in a nicer interface.

Update: Added a 100ms sleep (select) to stop the spinner using half the CPU.

#! perl -sw
use strict;
use Win32::Mutex;
$|++;

my $name = 'Spin_control';
if ( my $pid = fork() ) {
    my $n=0;
    my $mutex =Win32::Mutex->new(0,$name) or die $^E;
    while($mutex->wait() != -1) {
        $mutex->release();
        print chr(13) . 'Busy';
        print substr( '-\|/', $n++ % 4,1) . chr(8);
        select(undef,undef,undef,0.1); ## Added.
    }
}
elsif ( $pid == 0 ) {
    my $mutex = Win32::Mutex->open($name);
    $mutex->wait();
    print 'Not busy' . chr(13) for 1..1000;
    print $/;
    $mutex->release();
    my $count;
    $count++ for 1..1_000_000;
    $mutex->wait();
    print 'Counted to ', $count;
}
else {
    warn 'fork() failed';
}
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