Is it possible to differentiate if a client is running OSX or Windows in any other way than checking navigator.useragent property? I am developing a web app limited to OS X users and useragents are somewhat unreliable.
Check
window.navigator.platform
window.navigator as a whole should have more data.
You can use get_browser() PHP function to get the platform and other details.
You can get all detail by using $_SERVER variable in php.