osTicket is an open source trouble tickets script.
From the Author
osTicket is a widely-used open source support ticket system. It seamlessly integrates inquiries created via email and web-based forms into a simple easy to use multi-user web interface. Easily manage, organize and archive all your support requests and responses in one place while providing your clients with accountability and responsiveness they deserve.
Authors website: http://www.osticket.com/