When using the webform module, is it possible to get information on the submitter's device (Mac/Win/Android), browser version, etc.?
It appears webform allows a default value using %server variables, but only for authenticated users.


  In addition to %get and %post, the following super tokens may be used,
  though only with logged-in users: %server, %cookie, and %request. For
  example %server[HTTP_USER_AGENT] or %session[id].


For authenticated users, try adding a User Agent field with a default value of %server[HTTP_USER_AGENT]

If your form submissions come from anonymous users, you may need an alternative way to add the %server tokens.

Other $_SERVER variables documented here: http://php.net/manual/en/reserved.variables.server.php