Open source Ticketing systems

Orchard Collaboration

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

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

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 - MAC OS X

3 applications