Helpdesk - OTRS (win/linux)

OTRS, Open-source Ticket Request System, is a free and open-source trouble ticket system software package that a company, organization, or other entity can use to assign tickets to incoming queries and track further communications about them. It is a means of managing incoming inquiries, complaints, support requests, defect reports, and other communications.

http://en.wikipedia.org/wiki/OTRS