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.

Pure Chat - Pure Chat provides FREE live website support and sales chat without the hassle! It's web site chat, simplified.

Kapdesk - Kapdesk offers support teams with a helpdesk software to streamline support tasks.

Zendesk - Zendesk is a beautiful, lightweight help-desk solution.