Issuetrak - Issue tracking software for help desk and customer service
Solvvy - Highly intelligent customer support self-service solution via AI/ML/NLP science
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.
Whatfix - Whatfix Enterprise: Enhancing self-service capability of any web product
Kapdesk - Kapdesk offers support teams with a helpdesk software to streamline support tasks.
phpMyFAQ - phpMyFAQ is a world’s most popular mobile-friendly, feature-rich and open-sources FAQ software that uses PHP 5.