Issuetrak - Issue tracking software for help desk and customer service
Freshservice - Freshservice: the one-stop cloud solution for all your IT management needs.
Deskun - Deskun is a Help Desk system inside Gmail. It enables you to support customers directly from your mailbox, manage projects, and use free features for Gmail.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Kapdesk - Kapdesk offers support teams with a helpdesk software to streamline support tasks.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.