For help desk software, we presently use WHMCS, and find it to work well. We have had mixed success with the email to ticket system due to spam, but recommend using maxmind+fraudalert for orders to insure that we do not get clients with bad histories, like DMCA/SPAM
We currently use Kayako. It does it's job well but gives us quite a few advantages as we heavily customize all of our internal systems.
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