OTRS - Open source Ticket Request System
OTRS is an Open source helpdesk software with many features to manage customer telephone calls and e-mails. The system is built to allow your support, sales, pre-sales, billing, internal IT, helpdesk, etc. department to react quickly to inbound inquiries.
Proprietary alternative(s):
JIRA
Open Source alternative(s):
RT - Request Tracker
Saas alternative(s):
ZenDesk