I am quite interested in this Request Tracker (user: guest pass: guest) from Best practical.
Ok, I don’t think anything can beat the Debian BTS at present. But that is too Debian specific.
If you run an IT support company you need to be the layer / middle man between Debian and your customer.
Some other interesting packages :
phpgroupware-tts – The phpGroupWare trouble ticket system module
request-tracker1 – Request Tracker, a GPL‘d Trouble Ticket System
request-tracker3 – Extensible trouble-ticket tracking system
rt3-clients – Mail gateway and command-line interface to request-tracker3
rtfm – RT FAQ Manager
There is always Bugzilla, but I hate it’s interface.
Food for thought.