Jutda Helpdesk is an easy-to-use & open source trouble ticket system that is built with Django.
Whether the tickets are sent via the web interface or e-mail, the application can create the ticket & users can reply to e-mails to continue the conversation (e-mail piping).
It can be enabled to accept tickets from non-registered users which also makes it possible to be used as an advanced contact form.
Tickets can be separated into departments, product-groups, or any other classifications. Also, they can be escalated automatically between users by priority.
The application supports multiple RSS feeds & has an API for integration with 3rd party products.
P.S. Jutda Helpdesk is currently in alpha status yet very promising.
Requirements: Python 2.3+, Django
Website: http://www.jutdahelpdesk.com/
Demo: http://www.jutdahelpdesk.com/demo/
Download: http://www.jutdahelpdesk.com/download/
