"Project Issues" is your answer - that makes Projects work as a help desk. Everything else depends on your specific requirements.

But you migh be interested in the "Project and Services" community community project. I made a presentation for OpenDays introducing some helpdesk related features.

Have you looked in to the Issue Tracker app? I think it may have the functionality you need.

Alex, thanks for your response. I am not sure if it will do the way it currently is. I was hoping for something closer to the Helpdesk and Support module that is located in the After-Sale Services section of the Sales module.