Anonymantis is a set of PHP scripts that allows your users to report bugs that go straight into your Mantis bug tracker, without ever having to allow them any access to the tracker itself. In order to use Anonymantis, all you need to do is add an anonymantis user (mark the user as a 'developer') in Mantis, and enter in the appropriate configuration parameters in config.inc.php, and enjoy!
Anonymantis uses MantisConnect which can be downloaded here
The latest release of Anonymantis can be downloaded from here