Wikipedia has a useful comparison of issue-tracking systems, mostly IT focused though:

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

These might be closer to what you are looking for but I can't recommend them because I haven't tried them. GPLi has my vote for tech support.

http://osticket.com/

https://zammad.org

You could also consider a CMS (Wordpress, Drupal, etc.) help-desk plugin