Originally Posted by directfiesta

All Open Source:

http://www.helpcenterlive.com/
http://osticket.com/
http://www.phpsupporttickets.com ( free is for older releases )
http://www.dayanahost.com/phponline.cfm


then you have the paying one ( Kaiko, etv ... )

http://www.phplivesupport.com/
http://www.activecampaign.com/triolive/

and the best:

http://www.kayako.com/