module that loads either Win32::SerialPort or Device::SerialPort, although they both provide a very similar API

I've done something like that...not an "Any" module, but conditionally loading one or the other. You do need to wrap it in a BEGIN block and eval, due to the way "use" works:

#
# Use Win32::Serial port on Windows otherwise, use Device::SerialPort
#;
BEGIN 
{
   my $IS_WINDOWS = ($^O eq "MSWin32" or $^O eq "cygwin") ? 1 : 0;
   #
   if ($IS_WINDOWS) {
      eval "use Win32::SerialPort";
      die "$@\n" if ($@);
   } else {
      eval "use Device::SerialPort";
      die "$@\n" if ($@);
   }
}
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Then something like this when using it:

my $IS_WINDOWS = ($^O eq "MSWin32" or $^O eq "cygwin") ? 1 : 0;
if ($IS_WINDOWS) {
   $serial = new Win32::SerialPort ($port, 1);
} else {
   $serial = new Device::SerialPort ($port, 1);
}
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Somewhat ugly, but handy for anyone using my module. There's likely some more elegant way to do it.