Comparison of issue-tracking systems

https://en.wikipedia.org/wiki/Comparison_of_issue-tracking_systems

Others worth looking at (not in the list below) are sirportly and servicenow.

System
Apache Bloodhound
Assembla Tickets
Axosoft
Brimir
Bugzilla
Debbugs
FogBugz
Fossil
FusionForge
GNATS
Google Code Hosting
HP Quality Center
IBM Rational ClearQuest
JIRA
Kayako SupportSuite
Liberum Help Desk
MantisBT
Microsoft Dynamics CRM
org-mode
OTRS
Pivotal Tracker
Plain Ticket
Planbox
QuickBase
Redmine
Remedy Action Request System
Request Tracker
Roundup
StarTeam
Supportworks
SysAid
TargetProcess
Team Foundation Server
Teamwork
TechExcel's DevTrack
TestTrack
The Bug Genie
Trac
TrackerSuite.Net
Usersnap
Web Help Desk
Wrike
YouTrack
Zoho BugTracker