OTRS - Open Source Ticket Request System

OTRS, an initialism for 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.
We are using it Customer Support & successfully running from last 3 years.

The Open-source Ticket Request System (OTRS) is more than a mailing list notification system for ticket requests.

Every ticket generated by the system has persistence or "history" showing what happened to the ticket within its life cycle. OTRS has the ability to merge multiple requests about the same incident, thus making it possible to work on an incident rather than on singular requests.^[2] OTRS is a multiuser system which means that multiple agents may work simultaneously on the tickets in OTRS, reading the incoming messages, bringing them in order, and answering them. OTRS is highly scalable, capable of handling thousands of tickets per day and a nearly unlimited number of simultaneously working agents.

OTRS has integrated functionality for creating, reworking and searching FAQ texts. The FAQ texts may be incorporated into the agents' answers on tickets.

By using a multilingual web user interface, OTRS is usable independently from the respective operating systems since it is operated from a web browser. Furthermore, this facilitates the usage of OTRS by external agents or even customers participating in, working on or contributing to tickets.

OTRS establishes a framework of functions. For example, the incident handling system SIRIOS of BSI, Germany, is based on OTRS.

Software Download
Download the full versions of OTRS Help Desk and OTRS ITSM (the ITIL® V3 compliant IT Service Management solution). You'll also find the various OTRS extensions for download (all extensions on this page are published under the Affero General Public License V.3 and are available free of any license costs).

Content
Download a Stable Release
Download OTRS Extensions

Download other versions also from here

Documentation -

http://doc.otrs.org/3.1/en/html/

What's New in OTRS 3.1
The new release of OTRS is designed so that organizations can centralize their Customer Service and IT Service Management on OTRS: the newly designed Generic Interface takes back-end integration to your existing data systems to a new level. In addition, OTRS 3.1 has many new features that will benefit Agents and Admins alike on a daily basis.

Visit website -

http://en.wikipedia.org/wiki/OTRS 

http://www.otrs.com/en/open-source/ 

Screenshot -