HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Issuetrak - Issue tracking software for help desk and customer service
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
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.
HelpNinja - Simple & Affordable help desk
Kapdesk - Kapdesk offers support teams with a helpdesk software to streamline support tasks.