Orchard Collaboration is a free, open source ticketing system, project management and collaboration framework. It integrates with Orchard CMS and extends its features by allowing its users to collaboratively work on the content. (GPL)
Windows
osTicket is a widely-used open source support ticket system. It seamlessly integrates inquiries created via email, phone and web-based forms into a simple easy-to-use multi-user web interface. (GPL)
Cross-platform
OTRS is an Open source Ticket Request System (also well known as trouble ticket system) with many features to manage customer telephone calls and e-mails. (GPL)
Linux - FreeBSD - Windows - macOS
UVdesk Helpdesk is an open source ticketing systems with the following functionality: email piping, knowledgebase, modern SLA, automated rules, saved replies, agent privileges, live reporting, analytics, ticket types and unlimited support agents. (MIT)
Cross-platform
4 applications