By default, all projects in Pivotal Tracker are private and accessible only to users you explicitly invite, however, you can make a project “Public” from the Project Settings page.
Public projects are intended for use with open-source software development, or with any initiative that does not require data privacy. Public projects are free no matter how many members you invite to them, as they do not count towards project or collaborator limits on any plan.
Public projects can be accessed by anyone who knows the URL, in read-only mode, whether they are signed in to Tracker or not. However, only invited project members who are signed in to Tracker can make changes to a public project. Additionally, anyone can self-join public projects as a viewer (read-only member) and follow stories.