suggestions of Helpdesk software, request tracking - public domain or low cost

[trm at eskimo.com]

  I am seeking suggestions of Low cost or public domain Helpdesk software
which is web based and also sends out email messages was needed.

  Examples would be:
  - troubleticketexpress.com
  - perldesk.com


  Please provide suggestions, and some features you like about the
Helpdesk software. Please do not provide critics of other persons
suggestions.

  Thanks!

   Tim Mitchell
   Unix System Administrator
   trm at eskimo.com