Project privacy set to public. By default, its content is available to everyone (authenticated or not). Please note that more restrictive permissions might exist on some items.
When commenting on an artifact, Tuleap conveniently allows to tag a user using @ + username. However, those users are not notified of their mention, unless they're previously assigned to or on the CC list of the artifact.
It would be conventient to have an email notification whenever a user is mentioned on an artifact.