Add OS to Body Class

os-body-class.php

<?php 

function mv_browser_body_class($classes) {
    global $is_lynx, $is_gecko, $is_IE, $is_opera, $is_NS4, $is_safari, $is_chrome, $is_iphone;
    if($is_lynx) $classes[] = 'lynx';
    elseif($is_gecko) $classes[] = 'gecko';
    elseif($is_opera) $classes[] = 'opera';
    elseif($is_NS4) $classes[] = 'ns4';
    elseif($is_safari) $classes[] = 'safari';
    elseif($is_chrome) $classes[] = 'chrome';
    elseif($is_IE) {
      $classes[] = 'ie';
      if(preg_match('/MSIE ([0-9]+)([a-zA-Z0-9.]+)/', $_SERVER['HTTP_USER_AGENT'], $browser_version))
      $classes[] = 'ie'.$browser_version[1];
    } else $classes[] = 'unknown';
    if($is_iphone) $classes[] = 'iphone';
    if ( stristr( $_SERVER['HTTP_USER_AGENT'],"mac") ) {
         $classes[] = 'osx';
       } elseif ( stristr( $_SERVER['HTTP_USER_AGENT'],"linux") ) {
         $classes[] = 'linux';
       } elseif ( stristr( $_SERVER['HTTP_USER_AGENT'],"windows") ) {
         $classes[] = 'windows';
       }
    return $classes;
  }
  add_filter('body_class','mv_browser_body_class');

?>

http://wpsnipp.com/index.php/functions-php/browser-detection-and-os-detection-with-body_class/