This addon is a plugin. You need to extract it to your /plugins folder to install it.
Allows users that are already logged in to post anonymously by checking a box on the discussion/comment posting form.
Before installing Make sure you create your anonymous user in your Vanilla installation. This user can have any username you want, but the default is "Anonymous". If you would like to user something else, make sure you change line 15 of default.php.