Here’s a snip­pet of JS code that might come in handy if you, let’s say, would like to fil­ter out what type of con­tent to dis­play depend­ing on your web­site user’s OS. A real-life exam­ple would be hav­ing a down­load link show up to user’s who have a client that was only pub­lished on Win­dows.

// This script sets OSName variable as follows:
// "Windows"    for all versions of Windows
// "MacOS"      for all versions of Macintosh OS
// "Linux"      for all versions of Linux
// "UNIX"       for all other UNIX flavors 
// "Unknown OS" indicates failure to detect the OS

var OSName="Unknown OS";
if (navigator.appVersion.indexOf("Win")!=-1) OSName="Windows";
if (navigator.appVersion.indexOf("Mac")!=-1) OSName="MacOS";
if (navigator.appVersion.indexOf("X11")!=-1) OSName="UNIX";
if (navigator.appVersion.indexOf("Linux")!=-1) OSName="Linux";

document.write('Your OS: '+OSName);

Note: An alter­nate way can be found via PPK’s quirksmode.org