Open-source Help Desk and IT Service Management solution
OTRS is an Open Source Issue Tracking System. Currently OTRS is an acronym of "Open Technology - Real Service". Written mostly in Perl it is licensed unter the GNU Affero General Public License Version 3 (AGPL3).
It tracks Tickets in Queues and defines SLA for services. It has many large customers and offers a wide variety of customizations.
Source Code (Github): https://github.com/OTRS/otrs
See the main webpages : http://www.otrs.com/ http://www.otrs.org/
See the community site : http://www.otterhub.org/de/
Wikipedia: http://en.wikipedia.org/wiki/OTRS